Sahih Muslim Book 7, Hadith Number 2909.

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

Ibn ‘Umar (Allah be pleased with them) reported: I have not abandoned touching of Yamani corners (and kissing of) the Stone since I saw Allah’s Messenger (may peace be upon him) touching them both In hardship and ease.