Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) used to kiss the Black Stone and say: "I surely know that you are a stone; you neither harm nor benefit. But I saw Abu al-Qasim (peace and blessings be upon him) showing great care for you."
(b) In another narration: Sayyiduna Umar (may Allah be pleased with him) kissed the Black Stone and said: "I am kissing you, and I surely know that you are a stone," then he mentioned the rest of the narration.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9220