Musnad Ahmad Hadith 18330

Abu Wa'il (may Allah have mercy on him) says that once I was sitting with Abu Musa Ash'ari (may Allah be pleased with him) and Abdullah bin Mas'ud (may Allah be pleased with him). Abu Musa (may Allah be pleased with him) said, "O Abu Abdur Rahman! Tell me, if a person becomes impure and does not find water, will he remain in the state of janabah for a whole month and not be allowed to perform tayammum?" He replied, "No, even if water is not found for a month." Abu Musa (may Allah be pleased with him) said, "Then what will you do with the verse in Surah Ma'idah in which Allah Almighty says: 'If you do not find water, then perform tayammum with clean earth'?" Ibn Mas'ud (may Allah be pleased with him) replied, "If people are given this permission, they will start performing tayammum with earth and praying even in slight cold." Abu Musa (may Allah be pleased with him) asked, "Then what about the statement Ammar (may Allah be pleased with him) made to Umar (may Allah be pleased with him)?"