The Messenger of Allah ﷺ said:
“There has come to you Ramadhan, a blessed month, which Allah, the Mighty and Sublime, has enjoined you to fast. In it the gates of heavens are opened and the gates of Hell are closed, and every devil is chained up. In it Allah has a night which is better than a thousand months; whoever is deprived of its goodness is indeed deprived.”
[Nasai]
Definition: Sawm is to stay away from eating and drinking from Fajr till Maghrib during the month of Ramadhan.
Status: Fardh (obligatory)
Sawm is Fardh on:
The one who is Muslim.
The one who is Baaligh (reached puberty/physical maturity).
The one who is 'Aaqil (sane).
The following do not have to fast but will have to do Qadha (make it up):
The one who is so sick that fasting will worsen his condition and he knows this through past experiences or he was told by a skillful, trusted Muslim doctor.
The one is a traveler according to Islamic standards.
The woman who is going through menstruation or post-natal bleeding.
Faraaidh of Sawm:
To have Niyyah (Intention) of fasting by midday.
To stay away from everything that breaks the fast.
Sunan of Sawm:
To eat Sehri.
To break the fast immediately after sunset.
To perform Taraweeh Salaah at night.
To feed the poor and hungry.
To increase the reading of the Quran.
To observe I’tikaaf in the Masjid during the last ten days of Ramadhan.
Mustahabbaat (Virtous Acts) of Sawm:
To delay the Sehri till a little while before Fajr.
To break one’s fast with dates and if dates are not available, then water.
To make Niyyah (intention) the night before.
Makroohaat (Disliked Acts) of Sawm:
To chew plastic, rubber, or any such items.
To taste any food and drink, then to spit it out.
To collect saliva in the mouth and to swallow it.
To delay a Fardh Ghusl knowingly after Fajr.
To use toothpaste or tooth powder.
To complain of hunger and thirst.
To take the water too much up the nose when washing it.
To gargle more than necessary.
To argue or to use indecent words
To backbite, lie, curse, and other sins will be more severe.
Mufsidaat (Nullifiers) of Sawm:
Qadha will be necessary if anything was put by force into the mouth.
Qadha will be necessary if one swallows something that was stuck between the teeth if it was bigger than a grain. -Qadha will not be necessary if it was smaller than a grain. -Qadha will be necessary if he removes it then swallows it, regardless of its size.
Qadha will be necessary if one vomits a mouthful intentionally or returns vomit down the throat. -Qadha will not be necessary if one vomits a mouthful unintentionally.
Qadha will be necessary if swallowing items that are not food or medicine intentionally like pebbles, paper, etc. -Qadha will not be necessary if a fly, mosquito, or any other object goes down his throat unintentionally.
Qadha will be necessary if oil goes into the ear. -Qadha will not be necessary if water goes into the ear.
Qadha will be necessary if snuff is inhaled into the nose.
Qadha will be necessary if one swallows blood that is more than his saliva. -Qadha will not be necessary if one swallows his own saliva.
Qadha will be necessary if one eats and drinks forgetfully and then continues to eat and drink thinking that his fast is broken. -Qadha will not be necessary if one eats and drinks forgetfully and then continues to keep his fast after he remembers.
Qadha will be necessary if one eats or drinks mistakenly (while he remembers that he is fasting) like water going down the throat when gargling. -Qadha will not be necessary if dust or dirt goes down the throat.
Qadha will be necessary if one eats or drinks after Fajr or before sunset due to cloudy weather or a faulty clock and then realizing one’s mistake.
Qadha and Kaffarah will be necessary if one eats, drinks, or breaks the fast in any way without a valid reason. -Kaffarah means to fast for 60 days consecutively. If he is unable to do that, then he must feed 60 poor people two meals or give each of them the value of 3 ½ lbs of wheat.
Qadha and Kaffarah will be necessary if one applies surma on his eyes or oil on his head and then continues to eat and drink thinking that his fast is broken. -Qadha will not be necessary if one applies surma on his eyes, contact lenses, or oil on his head or body by itself.
Qadha and Kaffarah will be necessary if one drinks any medicine intentionally without a valid excuse. This includes an asthma pump, a nebulizer, and nose drops. -Qadha will not be necessary if one takes an injection, eye drops, or ear drops, or takes a blood test.
The Messenger of Allah ﷺ said:
“The five daily prayers, Jumu’ah to Jumu’ah, and Ramadhan to Ramadhan expiate for (the sins perpetrated) in between them, so long as one stays away from the major sins.”
[Muslim]