Ibn Mas'ud reported the Prophet as saying, "When I am gone copy those two of my companions, Abu Bakr and `Umar, follow the guidance of `Ammar, and hold fast to the injunction of Ibn Umm `Abd.'' Hudhaifa's version has "Believe what Ibn Mas'ud tells you" Instead of "Hold fast to the injunction of Ibn Umm `Abd." Tirmidhi transmitted it.