Musnad Ahmad 27:1163

Hashim ibn al-Qasim narrated to us, al-Layth narrated to us, from Yazid ibn Abdullah ibn Usama ibn al-Had al-Laythi, from Abdullah ibn Dinar, from Ibn Umar, that he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, the most righteous of righteousness is for a man to maintain ties with the people his father loved after he has passed away."