Tirmidhi

Explanation:
1:
That is, whoever made a vow (nadhar) and did not specify it by name, meaning he only said that if his wish is fulfilled, a vow is due upon him, then its expiation (kaffarah) is the same as the expiation for an oath (yamin).

Note:
(However, the phrase 'lam yusamm' is not authentic, and apart from the author, it is not found with anyone else (whereas Abu Dawood, taking this into consideration, has titled a chapter “Whoever makes a vow and does not specify it”). This is an addition from the author’s narrator “Muhammad Mawla al-Mughira,” who himself is an unknown (majhool) narrator; he is not present in the chains of others.)

The expiation (kaffarah) for an oath is explicitly mentioned in the Noble Qur’an, and it is: feeding ten needy people, or clothing them, or freeing a slave. If one is unable to do any of these three, then he must fast for three days. And this is also the expiation for a vow (nadhar). In expiation, sequence is not necessary; rather, whichever act is easier may be performed. If the vow is for a righteous deed and one has the ability to fulfill it, then the vow itself must be fulfilled. Expiation is only in the case when fulfilling the vow is not possible, or if the vow is for a sinful act.