Tosefta for Kiddushin 78:8

[With respect to the ritual involving two live birds to purify a metzora, see Lev. 14:4-8,] one who finds a nest shall not [use it to] purify a metzora, as it says "v'lakach" (i.e., "take" or "buy"). One who carries away the mother with her chicks, Rabbi Yehuda says, he is to be flogged, but need not send away the mother (Makkot 3:4), and the Sages say, he sends away [the mother] and is not flogged. This is the general rule: All negative commandments that require one to get up and perform [an act], one who [violates] it is not liable [for lashes]. A person must not take away the mother with her chicks, and even not to purify a metzora, because [the purification ceremony] will be performed through a transgression. § Rabbi Ya'akov says (see Hul. 142a:3-9), there is no commandment in the Torah whose reward is not stated next to it, and [as to which] the resurrection of the dead is [not] written in it, as it says, "Surely send away the mother [... so that it will be good for you]." Someone climbed to the top of a tree [and sent away the mother bird] and fell and died, and [another climbed] to the top of a building [and sent away the mother bird] and fell and died -- where is the goodness in that? [Rather,] it is said (Deut. 22:7), "so that it will be good for you" -- this is in the "good world" (i.e., this world) -- "and your days will be lengthened" -- this is in the "long world" (i.e., the eternity of the world to come).