اَللَّهُ أَكْبَرُ

Allahu 'Akbar

Allah is the Most Great. Allah's Messenger (ﷺ) performed Tawaf (of the Ka`ba) ending a camel (at that time the Prophet [ﷺ] had foot injury). Whenever he came to the Corner (having the Black Stone) he would point out towards it with a thing in his hand and say, "Allahu-Akbar." (The dua is Mentioned above)

Reference: Bukhari: 1613, 1632