Jami` at-Tirmidhi 877
جامع الترمذي#877SahihIbn Abbas narrated that:The Messenger of Allah said: "The Black Stone descended from the Paradise, and it was more white than milk, then it was blackened by the sins of the children of Adam
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiHasan
In-book reference: 9:70