Praise be to Allah.
Tawaaf around the Ka’bah is one of the pure rituals of worship, and the basic principle concerning rituals of worship is that they should be done as prescribed in the Qur’aan and Sunnah. It was narrated that the Messenger of Allaah (peace and blessings of Allaah be upon him) used to say Takbeer in Tawaaf every time he came in line with the Black Stone. Undoubtedly the worshipper comes in line with the Black Stone at the end of the seventh circuit, so it is Sunnah for him to say Takbeer as it is Sunnah for him to do so at the beginning of each circuit, when he comes in line with it – following the example of the Messenger of Allaah (peace and blessings of Allaah be upon him). He should also touch or kiss the Black Stone is he is able to.
And Allaah is the Source of strength. May Allaah send blessings and peace upon our Prophet Muhammad.