Maliks Muwatta Book 20, Hadith Number 113.

Section : Saluting the Corners during Tawaf.

Yahya related to me from Malik that he had heard that when the Messenger of Allah, may Allah bless him and grant him peace, had finished his tawaf of the House, prayed two rakas, and wanted to go to Safa and Marwa, he would salute the corner of the Black Stone before he left.