Sahih Bukhari

Narrated Ibn `Abbas:Allah's Messenger (ﷺ) performed the Tawaf (around the Ka`ba while riding his camel, and every time he reached the corner (of the Black Stone) he pointed at it with his hand and said, ""Allahu Akbar."" (Zainab said: The Prophet (ﷺ) said, ""An opening has been made in the wall of Gog and Magog like this and this,"" forming the number 90 (with his thumb and index finger)