Reference for Bava Metzia 6:7
הִלְוָהוּ עַל הַמַּשְׁכּוֹן, שׁוֹמֵר שָׂכָר. רַבִּי יְהוּדָה אוֹמֵר, הִלְוָהוּ מָעוֹת, שׁוֹמֵר חִנָּם. הִלְוָהוּ פֵּרוֹת, שׁוֹמֵר שָׂכָר. אַבָּא שָׁאוּל אוֹמֵר, מֻתָּר אָדָם לְהַשְׂכִּיר מַשְׁכּוֹנוֹ שֶׁל עָנִי לִהְיוֹת פּוֹסֵק עָלָיו וְהוֹלֵךְ, מִפְּנֵי שֶׁהוּא כְּמֵשִׁיב אֲבֵדָה:
If one lends another on a pledge, he (the lender) is a hired watcher, [whether he lent him and then took the pledge, or took the pledge and then lent him. And what is his "benefit"? The reward of a mitzvah.] R. Yehudah says: If he lent him money, he is an unpaid watcher, [R. Yehudah holding "the reward of a mitzvah" not to be relevant in this regard]; if he lent him fruits, he is a hired watcher, [for fruits tend to rot (and his "benefit" is anticipating fresh fruit in return). The halachah is not in accordance with R. Yehudah.] Abba Shaul says: One is permitted to rent out [to others] a poor man's pledge [entrusted with him], to set [its rental fee] and progressively [deduct from the poor man's) debt.], for it is as if he returns a lost object (to the poor man). [And this, only with a pledge whose rental is high and its depreciation (through use) low, such as hoe or spade, and the like. And this is the halachah.]