Abu Da'ud أبو داود السجستاني الأزدي · Fasting (Kitab Al-Siyam)

I heard Abu 'Amr al-Auza'i say: The word sirrahu means beginning of the month.

A man came to the Prophet (ﷺ) and said: I am undone. He asked him: What has happened to you ? He said: I had intercourse with my wife in Ramadan (while I was fasting). He asked: Can you set a slave free ? He said: No. He again asked: Can you fast for two consecutive months ? He said: No. He asked: Can you provide food for sixty poor people ? He said: No. He said: Sit down. Then…

When it was mentioned to Ibn Shihab (al-Zuhri) that fasting on Saturday had been prohibited, he would say: This is a Himsi tradition.

The Messenger of Allah (ﷺ) used to command us to fast the days of the white (nights): thirteenth, fourteenth and fifteenth of the month. He said: This is like keeping perpetual fast.

The sunnah for one who is observing i'tikaf (in a mosque) is not to visit a patient, or to attend a funeral, or touch or embrace one's wife, or go out for anything but necessary purposes. There is no i'tikaf without fasting, and there is no i'tikaf except in a congregational mosque.