Narrated Abdullah ibn Abbas: The Prophet ﷺ said: If anyone takes a vow but does not name it, its atonement is the same as that for an oath, if anyone takes a vow to do an act of disobedience, its atonement is the same as that for an oath, if anyone takes a vow he is unable to fulfill, its atonement is the same as that for an oath, but if anyone takes a vow he is able to fulfill, he must do so. Abu Dawud said: This tradition has been transmitted by Waki and others on the authority of Abdullah bin Saeed bin Abi al-Hind, but they traced it no farther back than Ibn Abbas.
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues:
This narration is mawquf (stopped at the Companion).
Therefore, it is not a proof in comparison to a marfu‘ (Prophetic) narration.
What is established from authentic marfu‘ narrations,
Its summary has been stated by Imam Shawkani in this way: If a specific vow (nazr) pertains to an act of righteousness but acting upon it is beyond one’s ability,
then the expiation (kaffarah) of an oath (qasam) is due in it.
And if it is within human ability and capacity, then fulfilling it is obligatory,
whether it pertains to the body or to wealth. And if the vow is for an act of disobedience (ma‘siyah),
then not fulfilling it is obligatory.
But in this case, expiation is not necessary. If the vow pertains to a permissible (mubah) matter and it is not beyond human ability,
then that vow will also be binding,
and expiation will also be obligatory in it.
Just as the female Companion who vowed to perform Hajj on foot, the Prophet (sallallahu alayhi wa sallam) forbade her from going on foot,
and ordered her to offer the expiation for riding.
And if the act is beyond human ability, then expiation is obligatory in it.
(Nayl al-Awtar, Chapters on Oaths, Their Expiation, Chapter: One Who Vows a Vow He Cannot Fulfill or Bear: 8/278)
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 3322