Sahih Al-Bukhari – Volume 3 – Book 30 – P.90

(16) CHAPTER. The Statement of Allah ” … And eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Saum (fast) till the nightfall…” (V.2:187) Narrated Al-Bara: The Prophet, peace be upon him, said as above.

Sahih Al-Bukhari – Volume 3 – Book 30 – P.89

(15) CHAPTER. The Statement of Allah: “It is made lawful for you to have sexual relations with your wives on the night of the  As-Saum (the fasts). They are Libãs [i.e., body cover or screen or Sakan (i.e., ‘you enjoy the pleasure of living with her’ — as in the Verse 7:189) — Tafsir At-Tabari], for you, and you are the same for them. Allah knows that you used to deceive yourselves, so He turned to you (accepted your repentance) and forgave you. So, now have sexual relations with them and seek that which Allah has ordained for you (offspring)…” (V.2:187)

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1915. Narrated Al-Bara:  It was the custom among the companions of Muhammad, peace be upon him, that if any of them was observing As-Saum (fast) and the food was presented [for Iftar – breaking his Saum  (fast)], but he slept before eating, he would not eat that night and the following day till sunset.

Qais bin Sirma Al-Ansari was observing Saum (fast) and came to his wife at the time of Iftar and asked her whether she had anything to eat. She replied, “No, but I would go and bring something for you.” He used to do hard work during the day, so he was overwhelmed by sleep and slept. When his wife came and saw him, she said, “Disappointment for you.” When it was midday on the following day, he fainted and the Prophet, peace be upon him, was informed about the whole matter; upon which the following Verses were revealed: “It is made lawful for you to have sexual relations with your wives on the night of As-Saum (the fasts)…”

So they were rejoiced greatly by it. And then Allah also revealed:
“…And eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)…” (V.2:187)  

Sahih Al-Bukhari – Volume 3 – Book 30 – P.88

(14) CHAPTER. Not to observe Saum (fast) for a day or two ahead of Ramadãn.

1914. Narrated Abü Hurairah:  The Prophet, peace be upon, said, “None of you should observe Saum (fast) from a day or two ahead of Ramadan unless he has the habit of observing Saum (Nawafil) (and if his fasting coincides with that day) then he can observe Saum (fast) on that day.”

Sahih Al-Bukhari – Volume 3 – Book 30 – P.86

1907. Narrated ‘Abdullãh bin ‘Umar : Allah’s Messenger, peace be upon him, said, “The month (can be) 29 nights (i.e., days), and do not fast till you see the crescent-moon, and if the sky is overcast, then complete Sha’ban as thirty days.”

Sahih Al-Bukhari – Volume 3 – Book 30 – P.85

(10) CHAPTER. As-Saum (the fasting) (is recommended) for those who fear committing illegal sexual acts, i.e., those who are unmarried.

1905. Narrated ‘Alqãma: While I was walking with ‘Abdullãh:  he said, “We were in the company of the Prophet, peace be upon him,  and he said, ‘He who can afford to marry should marry, because it will help him to lower his gaze (from looking at forbidden things and other women), and save his private parts (from committing illegal sexual acts etc.), and he who cannot afford to marry is advised to observe Saum (fasting), as Saum (fasting) will restrain his sexual power.”

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(9) CHAPTER. Should one say, “I am observing Saum (fast)” on being abused?

1904. Narrated Abu Hurairah:  Allah’s Messenger, peace be upon him,  said, “Allah said, ‘All the deeds of Adam’s sons (people) are for them, except Saum (fasting) which is for Me, and I will give the reward for it.’ Observing Saum (fast) is a shield or protection (from the Hell-fire and from committing sins). If one of you is observing Saum (fast), he should avoid sexual relation with his wife and quarreling, and if somebody should fight or quarrel with him, he should say, ‘I am observing Saum (fast).’ By Him in Whose Hands my soul is, the smell coming out from the mouth of a fasting person is better before Allah than the smell of musk. There are two pleasures for the person observing Saum, one at the time of Iftãr (breaking his fast), and the other at the time when he will meet his Lord; then he will be pleased because of his Saum (fasting) .”

Sahih Al-Bukhari – Volume 3 – Book 30 – P.84

(8) CHAPTER. Whoever does not give up lying speech (false statements (i.e., telling lies) and acting on those while observing Saum (fast).

1903. Narrated Abu Hurairah: The Prophet, peace be upon him,  said, “Whoever does not give up lying speech (false statements) and acting on those lies and evil actions etc., Allah is not in need of his leaving his food and drink [i.e., Allah will not accept his Saum (fasting)]”.