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.'" (DE)
English reference (DE): Vol. 3, Book 11, Hadith 2109 (DE)
Arabic reference (DE): Book 11, Hadith 2187 (DE)