Sunan Ibn Majah
2109
Sahih+3

It was narrated from Abul-Ahwas 'Awf bin Malik Al- Jushami that his father said:"I said: 'O Messenger of Allah, my cousin comes to me and I swear that I will not give him anything or uphold the ties of kinship with him.' He said: 'Offer expiation for what you swore about

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi