A man once said to Saʿīd ibn al-Musayyab, “I have never met anyone more scrupulously God-fearing than So-and-so.”
Saʿīd replied, “Have you ever seen ʿAlī ibn al-Ḥusayn?”
“No,” the man answered.
Saʿīd said, “Then you have never seen anyone more scrupulous than he.”

Sufyān ibn ʿUyaynah related, on the authority of al-Zuhrī, who said:
“I entered upon ʿAlī ibn al-Ḥusayn and he asked, ‘Zuhrī, what were you discussing?’
I replied, ‘We were reviewing the rulings on fasting, and my companions and I had agreed that no fast is obligatory except the month of Ramadan.’
He said, ‘Zuhrī, it is not as you have said. Fasting (ṣawm) is of forty kinds: ten of them are obligatory with the same weight as the fast of Ramadan; ten are forbidden; fourteen are optional—one may observe them or leave them; the fast of a vow (nadhr) is obligatory; and the fast observed during retreat (iʿtikāf) is obligatory.’

Al-Zuhrī continued: I said, ‘Explain them for us, O son of the Messenger of Allah ﷺ.’
He said:

“As for the obligatory fasts: the fast of Ramadan; two consecutive months for unintentional manslaughter when one cannot free a slave; three days as expiation for breaking an oath when one cannot provide the prescribed food; the fast required for shaving the head (while in a state of consecration); the fast for the blood of tamattuʿ for whoever cannot offer a sacrificial animal; and the fast that compensates for hunting while in a state of consecration— the game is assessed at its value and that amount is then converted into wheat.

“As for the fasts in which the person has a choice, they are: fasting on Monday and Thursday; six days of Shawwāl after Ramadan; fasting on the Day of ʿArafah; and fasting on the Day of ʿĀshūrāʾ—one may observe them or omit them.

“As for a fast requiring permission (ṣawm al-idhin): a woman is not to perform a voluntary fast without her husband’s consent, and the same ruling applies to a male or female slave.

“As for the forbidden fasts: fasting on the day of Fitr and the day of Aḍḥā; the three days of Tashrīq; the ‘day of doubt’ at the start of Ramadan, for we have been forbidden to fast it for Ramadan; the fast of wiṣāl (continuous fasting without breaking); the fast of silence; the fast of a vow undertaken for a sinful act; the fast of the entire year; and the fast of a guest—he must not fast voluntarily without the host’s permission.
The Messenger of Allah ﷺ said, ‘Whoever lodges with a people must not undertake a voluntary fast without their permission.’ (1)

“As for the fast of dispensation (ibāḥa): whoever eats or drinks forgetfully, his fast is still valid.

“Regarding the fast of the sick person and the traveler, some have said: he must fast; others have said: he must not; others have said: he may choose.
Our position is that he breaks the fast in both cases, and if he does fast while traveling or ill, he must make it up later.” (2)

[Among those who died this year was] Abū Bakr ibn ʿAbd al-Raḥmān ibn al-Ḥārith (3) ibn Hishām ibn al-Mughīrah ibn ʿAbd Allāh ibn ʿUmar ibn Makhzūm, the Qurayshī from Madinah—one of the seven jurists of the city. It is said his given name was Muḥammad; it is also said that his given name was Abū Bakr and his honorific Abū ʿAbd al-Raḥmān. The soundest view is that his name and his kunya were one and the same. He left many children and brothers, and he was a distinguished Successor (tābiʿī).