Nafi' (may Allah have mercy on him) narrated: I saw Sayyiduna Ibn Umar (may Allah be pleased with them both) touch the Black Stone with his hand and kiss his hand, and he said: "I have not abandoned it since I saw the Prophet (peace and blessings be upon him) doing it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9226