Midrash for Numbers 19:16

2) "and one who carries them": What is the intent of this? I might think that only merkav alone confers tumah by being carried. Whence do I derive the same for mishkav and moshav? (But a verse is not necessary for this.) I know it a fortiori, viz.: It merkav, which does not confer tumah upon garments by being touched, does confer tumah upon garments by being carried, then mishkav and moshav, which do confer tumah upon garments by being touched, how much more so do they do so by being carried! — (No,) this is refuted by the upper board and the side board of a coffin (viz. Bamidbar 19:16), which do confer tumah upon garments by being touched, but which do not do so by being carried.

6) "the flesh of the zav": and not a detached bone, and not detached flesh. How much more so is (a bone or flesh) detached from one that is tahor, tahor. How, then, am I to understand (Bamidbar 19:16): "or the bone of a man or a grave"? That refers to a limb detached form a living man.

Rabbi Levitas, a man of Jamnia, said: Unless the father of a leprous person spit in his face, he will not be healed, as it is said, "And the Lord said unto Moses, If her father had but spit in her face, would she not be ashamed seven days?" (Num. 12:14). Hence (the sages) say: A male afflicted with unclean issue (needs) seven (days for his purification); a woman with an issue (requires) seven (days' separation); a menstruant (needs) seven (days of purification); one made unclean through a corpse (needs) seven (days of purification); a mourner (mourns for) seven (days); the wedding feast (lasts) seven (days); and a leprous person (requires) seven (days' separation). (Whence do we know that) a male with an unclean issue (requires) seven days (for his purification)? || (Because it is said,) "And when he that hath an issue is cleansed of his issue, then he shall number to himself seven days for his cleansing" (Lev. 15:13). Whence do we know that a woman with an issue (requires) seven (days of purification)? Because it is said, "But if she be cleansed of her issue, then she shall number to herself seven days, and after that she shall be clean" (Lev. 15:28). Whence do we know that a menstruant (requires) seven (days of separation)? Because it is said, "She shall be in her separation seven days" (Lev. 15:19). "Her separation" (or impurity) thou dost not read, but "in her impurity"; because Rabbi Ẓe'era said: The daughters of Israel have made the Law exceptionally stringent for themselves, so that if they see a blood stain of the size of a mustard seed they observe on its account seven days, after that they are cleansed (of their issue of blood). Whence do we know that one made unclean through a corpse (needs) seven (days of purification)? Because it is said, "And whosoever in the open field toucheth one that is slain with a sword, or a dead body… shall be unclean seven days" (Num. 19:16). Whence do we know that the mourner (mourns for) seven (days)? Because it is said, "And he made a mourning for his father seven days" (Gen. 50.10). Whence do we know that the (bridal) banquet (lasts) seven days? Because it is said, "Fulfil the week of this one…. And Jacob did so, and fulfilled her week" (Gen. 29:27, 28). Whence do we know that a leper (keeps) seven (days of purification)? From Miriam, as it is said, "And Miriam was shut up without the camp seven days" (Num. 12:15).