Is the day upon which a person converts to Islam during Ramadan required to be fasted and made up?
General Chapter
Al-Mughni
Book of Fasting
Primary text
The one who converts on a day during the month is required to observe abstinence for the remainder of that day and must make up that day later. This is the explicit position of Ahmad, and it is the view of Majishun and Ishaq. The rationale is that upon conversion, one has reached a portion of the prescribed time for the act of worship, thus making it obligatory, just as reaching a portion of the prayer time necessitates observing it.
Supporting text
Malik, Abu Thawr, and Ibn al-Mundhir state that there is no make-up required because the convert did not witness the prescribed time while being obligated to observe the act, analogous to someone who converts after the day has ended. This view is also attributed to Ahmad.