Мидраш к Бамидбар 12:14

1) kal vachomer (a fortiori): (Bamidbar 12:14): "And the L–rd said to Moses: Now if her (Miriam's) father had spat in her face, would she not be in shame for seven days!" — Kal vachomer, if the Shechinah does so, it should be fourteen days! (see Tosfoth, Bava Kamma 25a). But it suffices that a kal vachomer deduction parallel what it is deduced from; therefore, (Bamidbar 12:14): "Let her be sequestered seven days outside the camp, and then let her be gathered in."

2) gezeirah shavah (Identity): It is stated in respect to a shomer sachar (a hired watchman) (Shemoth 22:9): "The oath of the L–rd shall be between both, that he (the watcher) did not send his hand against the deposit of his neighbor," and, in respect to a shomer chinam (one who watches gratis) (Shemoth 22:7): "that he did not send his hand, etc." Just as in the instance of a shomer sachar, in which it is written "that he did not send his hand," the heirs (of the watcher) are exempt (from an oath that their father did not send his hand, etc., it being written: "The oath of the L–rd shall be between both" [the owner and the watcher — and not between the heirs]), so, in the instance of a shomer chinam, where it is written "that he did not send his hand," the heirs are exempt.

R. Phinehas the priest, the son of Hama and R. Judah the son of Shalum asked: What is meant by gather yourselves together (he’asfu)? It means purify yourselves, as stated in the verse: Let her be shut up within the camp seven days, and after that she shall be purified (te’asef) (Num. 12:14). Another interpretation of gather yourselves. He counted them as elders, as is said: Gather unto me the seventy of the elders of Israel (Num. 11:16).