What is the ruling on dyeing hair black, and is it true that one of the Companions dyed his hair with it?

The ruling on dyeing hair black has been previously addressed. Among the Companions who dyed their hair black were Uthman, Al-Hasan, Al-Husayn, and Uqbah ibn Amir. The Salaf differed on dyeing: some considered refraining from it better, while others considered dyeing better. Most of those who dyed did so with yellow (henna), and a group dyed with black. The most correct and consistent with the Sunnah is the prohibition of dyeing with black due to the Prophet's (peace and blessings be upon him) saying: "And avoid black." As for those Companions from whom it is reported that they dyed with black, it is either that the narrator was mistaken, or that the Companion had not been informed of the prohibition.