The Messenger of Allah ﷺ said, "The finest act of kindness is for a person to maintain ties with his father's beloved friends after his father has passed away."
حدثنا هاشم بن القاسم حدثنا الليث عن يزيد بن عبد الله بن أسامة بن الهاد الليثي عن عبد الله بن دينار
قال رسول الله ﷺ إن أبر البر صلة المرء أهل ود أبيه بعد أن يولي
Its isnad is sahih. Muslim also related it, 2:277, through Ibrahim bin Saad and Layth, from Ibn Hadi, at length, within a story. Suyuti also attributed it in Jami Saghir, 2158, to Bukhari in Adab al-Mufrad, as well as to Abu Dawud and Tirmidhi. The longer version will come later through Layth as well, 5653.