Abis bin Rabi'ah says that I once saw Sayyiduna Umar (may Allah be pleased with him) kissing the Black Stone and addressing it, saying: "I know that you are a stone, but I am still kissing you. If I had not seen the Prophet (peace and blessings be upon him) kissing you, I would never have kissed you."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 176