"The Prophet (sal-Allaahu 'alayhe wa sallam) circled the Ka'bah on a camel, every time he reached the black stone he would point to it with something (his staff) and say:

اللَّهُ أَكْبَرُ

Allah is the Most Great.

Allaahu 'Akbar.

Al-Bukhari,,cf. Al-Asqalani, Fathul-Bari 3/476. See also 472. The 'something' that was referred to in this Hadith was a cane.