מדרש על שמות 22:9

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.

5) prat ukllal (specific-general): (Shemoth 22:9): "If a man give to his neighbor an ass or an ox or a lamb — specific; "or any beast to watch" — general: specific-general — the general adds to the specific.