Sahih Muslim
The Book of Pilgrimage (Kitab Al-Hajj)
Book Number: 007 / Hadith Number: 2910
NAfi' (Allah be pleased with him) reported: I saw'lbn '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.