Roza (Fasting)
In Sharia, Roza (fasting) is defined as abstaining from eating, drinking, and fulfilling sexual desires from Subh Sadiq (dawn) until sunset (the sun sets) with the intention of worship.
The only obligatory fast is that of Ramadan; all other fasts are Wajib (necessary), Sunnah (recommended), Mustahab (desirable), and Nafl (voluntary).
The fast of Ramadan is obligatory for every sane, adult Muslim man and woman.
Fasting is not obligatory for boys and girls until they reach puberty; if they fast, it is permissible and a cause of reward. If underage children start fasting and then break it, they are not required to make up for it. If an underage boy or girl reaches puberty before Subh Sadiq, it is obligatory for them to fast on that day. It is permissible to take medication to stop menstruation in order to fast, but it is medically harmful, so it should be avoided.
Niyyat (Intention) for Roza
Having the Niyyat (intention) is necessary for the fast to be valid; the fast is not valid without the intention.
The intention for the fast of Ramadan is valid from the night before, and it is also valid at the time of Sehri, i.e., before Subh Sadiq. If a person could not make the intention at night or before Subh Sadiq due to sleeping or any other reason, they can make the intention for the fast until Nisf al-Nahar Shari (midday according to Sharia). If a person cannot make the intention for the fast until Nisf al-Nahar Shari, then their intention is not valid, and they are required to make up for that fast.
Note! Nisf al-Nahar Shari is half the time between Subh Sadiq and sunset.
Niyyat (intention) is the name of the heart's intention; uttering the words of the intention is correct, but not necessary. If a person makes the intention in their heart and does not utter the words, it is also permissible.
Sehri
Eating Sehri is Sunnah and a cause of blessing. The time for Sehri is the night; you can eat Sehri as long as it is night. The time for Sehri ends when the night ends. The night lasts until Subh Sadiq; as soon as Subh Sadiq occurs, the time for Sehri ends. Some people continue to eat until the Fajr Adhan and think that they can eat and drink until the Fajr Adhan; this is not permissible, and the fast of such people is not valid because the Fajr Adhan occurs after the rising of Subh Sadiq, and the last time for Sehri is the rising of Subh Sadiq.
Mufsidat-e-Saum (Things that invalidate the fast)
Intentionally eating or drinking invalidates the fast, and Qaza (making up the fast) is required along with Kaffarah (expiation). Having intercourse with one's wife invalidates the fast, and both Qaza and Kaffarah are required. If a woman experiences menstruation or postpartum bleeding while fasting, the fast is invalidated. If a man ejaculates while kissing or caressing his wife while fasting, the fast is invalidated, and only Qaza is required, not Kaffarah. Smoking cigarettes invalidates the fast. Using Naswar (snuff) invalidates the fast. Using an inhaler during fasting invalidates the fast. If a loop is inserted into a woman's vagina for contraception while fasting, the fast is invalidated. If a doctor inserts a wet hand into a woman's vagina to diagnose a disease or estimate the duration of childbirth, the fast is invalidated. Using Beedi, cigarettes, and Huqqa while fasting invalidates the fast. Putting medicine inside the ear and nose during fasting invalidates the fast. If smoke is intentionally inhaled into the mouth while fasting, the fast is invalidated. If a person intentionally vomits a mouthful while fasting, the fast is invalidated; vomiting a mouthful means that it is difficult to stop or swallow it back. If a person eats or swallows something that is not usually eaten, such as soil, etc., while fasting, the fast is invalidated. If a person intentionally inhales smoke or dust into their throat while fasting, the fast is invalidated. If a person swallows their beloved's saliva while fasting, the fast is invalidated, and both Qaza and Kaffarah are required, and if they swallow someone else's saliva, the fast is invalidated, and only Qaza is required.
Things that do not invalidate the fast
If a fasting person eats or drinks something by mistake, the fast is not invalidated; similarly, if they have intercourse by mistake, the fast is not invalidated. Ejaculation does not invalidate the fast. If a doctor inserts a dry hand into a woman's vagina to diagnose a disease or estimate the duration of childbirth, the fast is not invalidated. Applying oil and smelling perfume does not invalidate the fast; similarly, applying Surma (kohl) does not invalidate the fast, even if its effect appears in the nasal discharge or saliva. Sleeping with one's spouse and kissing, etc., does not invalidate the fast, but it is Makrooh (undesirable) if there is a fear of intercourse. Swallowing saliva while fasting does not invalidate the fast. If a person needed to perform Ghusl (ritual bath) at night but did not perform it and remained in that state, the fast is valid. Vomiting unintentionally does not invalidate the fast. If a person tastes something and spits it out while fasting, the fast is not invalidated. If smoke or dust enters the throat unintentionally while fasting, the fast is not invalidated. A person should use Miswak (tooth stick) while fasting, whether it is fresh or dry; however, if they clean their teeth with toothpaste and Manjan (tooth powder), the fast is not invalidated, but it is Makrooh; however, if its particles enter the throat, the fast is invalidated. Giving blood while fasting does not invalidate the fast. Receiving blood transfusions while fasting due to necessity does not invalidate the fast. Dialysis and Angiography while fasting do not invalidate the fast. Blood tests while fasting do not invalidate the fast. Receiving glucose drips does not invalidate the fast.
Qaza and Kaffarah
Fasting is obligatory for every sane, adult Muslim man and woman; if a person does not fast or breaks the fast for any reason, they are required to make up for that fast. However, in some cases of breaking the fast, Kaffarah is also required along with Qaza. See the conditions for Kaffarah below.
(1) The person breaking the fast must be sane and adult; if a child breaks the fast, neither Qaza nor Kaffarah is required. (2) The fast that is broken must be an Ada (performed on time) fast of the month of Ramadan; if it is a Nafl fast of other days besides Ramadan, or a Qaza fast of Ramadan, Kaffarah is not required. (3) It must be broken intentionally; if the fast is broken by mistake or due to forgetfulness, Kaffarah is not required. (4) If the fast is broken due to sexual desire, it is necessary that intercourse has taken place; if ejaculation occurs only from kissing or caressing, or from masturbation, Kaffarah is not required. (5) If the fast is broken by eating or drinking, it is necessary that the thing eaten is used as food, medicine, pleasure, or natural desire; if someone eats soil, Kaffarah is not required. (6) The fast must be broken of one's own free will; if it is broken due to a threat of death or mutilation, Kaffarah is not required. (7) The fast must be broken without a valid excuse; if someone breaks the fast due to a severe excuse, Kaffarah is not required.
If multiple fasts in the same Ramadan are broken by eating, drinking, or intercourse, one Kaffarah is sufficient. And if multiple fasts of different Ramadans are broken by eating and drinking, one Kaffarah is sufficient, but if multiple fasts of different Ramadans are broken by intercourse, a separate Kaffarah is required for each Ramadan.
If several fasts are missed, it is permissible to make up for all of them together, and it is also correct to do so intermittently.
The Kaffarah for fasting is to fast for two consecutive months; if even one fast is missed in between, it must be started again from the beginning. If fasting is started from the first date of the Islamic month, then fast continuously for two months according to the Islamic calendar; whether the month has 29 or 30 days. And if the fast is started from the middle of the month, then it is necessary to complete sixty days. If a woman experiences postpartum bleeding during the performance of Kaffarah, the Kaffarah will not be fulfilled and must be started anew. And if menstruation occurs during the performance of Kaffarah, there will be no deficiency in the Kaffarah, but fasting should be started immediately after becoming pure.
If one does not have the strength to fast for sixty consecutive days, then feed sixty poor people two meals a day to their fill.
The above-mentioned issues are taken from the following books.
Tuhfa Mah Ramadan al-Mubarak (Mufti Mubeen ur Rehman Sahib, Pakistan)
Mah Ramadan ke Fazail wa Ahkam (Mufti Muhammad Rizwan, Pakistan)
Masail Roza (Maulana Muhammad Rifat Sahib Qasmi, Ustad Darul Uloom Deoband)