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 'Abd Allah b. Sa'id b. Abi al-Hind, but they traced it no farther back than Ibn 'Abbas.
The Messenger of Allah (ﷺ) as saying: The atonement for a vow is the same as for an oath. Abu Dawud said: This tradition has also been transmitted by 'Amr b. al-Harith from Ka'b b. 'Alqamah, from Ibn Shamasah on the authority of 'Uqbah.
That 'Umar said: Messenger of Allah, I took a vow in pre-Islamic times that I would stay in the sacred mosque (Masjid Haram) as a devotion (i'tikaf). The Prophet (ﷺ) said: Fulfill your vow.