Uthman bin 'Asim bin Husayn عثمان بن عاصم بن حصين أبو حصين · Fasting (Kitab Al-Siyam)

The Prophet (ﷺ) as saying: If anyone dies when some fast is due from him (i.e. which he could not keep) his heir must fast on his behalf. Abu Dawud said: This applies to the fast which a man vows ; and this is the opinion of Ahmad b. Hanbal.

The Prophet (ﷺ) used to observe I'tikaf during the last ten days of Ramadan. Nafi' said: 'Abd Allah (b. 'Umar) showed me the place in the mosque where Messenger of Allah (ﷺ) used to observe I'tikaf.