Mishnayos Chullin Perek 12 Mishnah 5

A person may not take the mother bird with the offspring even if he takes the mother for use as part of the ritual to purify the leper. The mishna compares the reward for performing the mitzva of sending away the mother bird from the nest to the reward for performing other mitzvot: And if with regard to the sending away of the mother bird, which is a mitzva whose performance is simple, as it entails a loss of no more than an issar, i.e., the value of the mother bird, the Torah says: “That it may be well with you, and that you may prolong your days” (Deuteronomy 22:7), it may be derived by a fortiori inference that the reward is no less for the fulfillment of the mitzvot in the Torah whose performance is demanding.

לֹא יִטֹּל אָדָם אֵם עַל הַבָּנִים, אֲפִלּוּ לְטַהֵר אֶת הַמְּצֹרָע. וּמָה אִם מִצְוָה קַלָּה שֶׁהִיא כְאִסָּר, אָמְרָה תוֹרָה (דברים כב), לְמַעַן יִיטַב לָךְ וְהַאֲרַכְתָּ יָמִים, קַל וָחֹמֶר עַל מִצְוֹת חֲמוּרוֹת שֶׁבַּתּוֹרָה: