Is wearing black upon the death of a relative an innovation or proven in the Sunnah?

Wearing black upon the death of someone has not been established in the Sunnah, and scholars have considered it an innovation (bid'ah).

Sheikh Ibn 'Uthaymeen was asked about the ruling on women following funeral processions and wearing black clothes, and he replied: "It is forbidden for women to follow funeral processions due to their lack of patience and because it exposes them to temptation and mixing with men. As for wearing black during a calamity, it is among the innovations."

He also said: "Designating a specific dress for mourning is, in our view, an innovation, and it may indicate a person's discontent with Allah Almighty's decree."

He further mentioned: "Wearing black as a sign of mourning for the dead is an innovation and an outward display of grief. It is similar to tearing garments and slapping cheeks, from which the Prophet (peace be upon him) disavowed the doer, as he said: '(He is not one of us who tears garments, slaps cheeks, and calls with the call of Jahiliyyah).' "