The Holy Quran, Chapter 2, verses 183-185:
O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous –
[Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] – then an equal number of days [are to be made up]. And upon those who are able [to fast, but with hardship] – a ransom [as substitute] of feeding a poor person [each day]. And whoever volunteers excess – it is better for him. But to fast is best for you, if you only knew.
The month of Ramadhan [is that] in which was revealed the Qur’an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey – then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful.
O Allah! Make the months of Rajab and Sha’ban blessed for us, and let us reach the month of Ramadan (i.e. prolong our life up to Ramadan, so that we may benefit from its merits and blessings) [Narrated by at-Tabarani and Ahmad]
Allah (swt) says in a hadith qudsi, “Every deed of the son of Adam is for him except fasting; it is for Me and I shall reward for it…” (Bukhari, Muslim).
“Whosoever fasts in Ramadan with faith and seeking Allah’s reward, all his past sins are forgiven.” [Agreed upon]
I heard Allah’s Messenger (ﷺ) saying regarding Ramadan, “Whoever prayed at night in it (the month of Ramadan) out of sincere Faith and hoping for a reward from Allah, then all his previous sins will be forgiven.” (Bukhari)
“Umrah during Ramadan is equivalent to Hajj.” (Ibn Majah)
“Whoever gives iftaar to one who is fasting will have a reward like his, without that detracting from the reward of the fasting person in the slightest.” (Sahih Tirmidhi)
The Prophet (pbuh) said: “Whoever does not give up false speech and acting upon it and offensive speech and behaviour, Allah has no need of his giving up his food and drink.” (Bukhari)