Shiyim bin Bitan says that Hazrat Muslamah bin Makhlad (may Allah be pleased with him) assigned Hazrat Ruwaifi' bin Thabit (may Allah be pleased with him) a responsibility in a low-lying area of land. So we traveled with him, then Hazrat Ruwaifi' (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said to me, "O Ruwaifi'! It may be that you live a long life, so inform people that whoever ties a knot in his beard, or hangs a string around his neck, or performs istinja (purification) with the dung or bone of an animal, then Muhammad (peace and blessings be upon him) is free from such a person."