It is narrated from Hazrat Abu Saeed Khudri (may Allah be pleased with him) that once Hazrat Abu Musa Ash'ari (may Allah be pleased with him) greeted Hazrat Umar (may Allah be pleased with him) three times, but did not receive permission, so he returned. Hazrat Umar (may Allah be pleased with him) sent a messenger after him asking why he had left. He replied that he had heard the Holy Prophet (peace and blessings be upon him) say: When any one of you greets three times and does not receive a reply, he should return.