Sahih Muslim Book 7, Hadith Number 2910.

Chapter : Excellence of touching the two corners (Rukunain al- Yamaniyain) in Tawaf.

Nafi’ (Allah be pleased with him) reported: I saw’ Ibn ‘Umar (Allah be pleased with them) touching the Stone with his hand and then kissing his hand and he said: I have never abandoned it since I saw Allah’s Messenger (way peace be upon him) doing It.