The Messenger of Allah ﷺ said, "The Black Stone descended from Paradise whiter than milk, but the sins of the children of Adam blackened it."
قال رسول الله ﷺ: نزل الحجر الأسود من الجنة، وهو أشد بياضا من اللبن فسودته خطايا بني آدم.
Tirmidhi (877) narrated it from Qutayba, who said, Jareer told us, from Ata bin Saaib, from Saeed bin Jubayr, from Ibn Abbas, and he related it. Tirmidhi said, "Hasan sahih." Ibn Khuzayma (2733) graded it sahih and narrated it through the route of Jareer and Ziyad bin Abdullah, both of them from Ata bin Saaib with the same wording. The hadith is mentioned in detail in the book on Hajj.