what is needed to complete the expiation, and then fasted in place of the remainder, it would not suffice him, because it is a substitute in the expiation, and therefore it is not completed by it, like other substitutes with what they replace. Furthermore, fasting is even further removed from feeding and clothing than emancipation is; so if it is not permissible to complete one of the two types of the replaced matter with the other, then completing it with a substitute is even more worthy of exclusion. If it is said: "This is invalidated by the case of wudu (ablution) and ghusl (full bath) with tayammum (dry ablution)." We respond: Tayammum does not serve as a partial substitute for a portion of the purification; rather, it serves as a substitute for the entirety of it, and here, if he were to perform the entire fast, it would suffice him.

1826 - Issue: He said: (And whoever enters into the fast, then becomes affluent, is not required to exit the fast for the purpose of emancipation or feeding, unless he wishes to.)

There are two parts to this issue:

The first part: That if he has begun the fast, and then becomes capable of emancipation, feeding, or clothing, he is not obligated to return to them. This is narrated from al-Hasan and Qatadah. This is also the position of Malik, al-Shafi'i, Ishaq, Abu Thawr, and Ibn al-Mundhir. It is narrated from al-Nakha'i and al-Hakam that he is obligated to return to one of them. This is the position of al-Thawri and the companions of reasoning (Ashab al-Ra'y); because he became capable of the original requirement before completing the substitute, so he is obligated to return, like one performing tayammum who becomes capable of water before completing his prayer. Our position is that it is a substitute that is not invalidated by the capability to perform the original, so he is not obligated to return to the original after having commenced with the substitute, just as if one performing tamattu' (a type of Hajj) who is unable to provide the sacrificial animal begins fasting the seven days; he does not exit the fast, without disagreement. The proof that the substitute is not invalidated is that the substitute is the fast, and it is valid alongside his capability [to perform the original] by consensus. It differs from tayammum, as tayammum is invalidated by the capability to use water after he has finished it. Furthermore, returning to water for purification involves no hardship, due to its ease, whereas with the expiation, it is burdensome to combine two duties, and mandating a return leads to...