Musnad Abu Ya'la al-Mawsili 154:39

Hadaba ibn Khalid narrated to us, Hazm narrated to us, from Thabit, from Abu Burdah, who said: I came to Medina. Then Abdullah ibn Umar came to me and said: "Do you know why I came to you?" I said: "No." He said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: 'Whoever wishes to maintain ties with his father in his grave, let him maintain ties with his father's brothers after him.' And there was brotherhood and affection between my father, Umar, and your father, so I wanted to maintain that."