וַיֹּ֤אמֶר יוֹסֵף֙ הָב֣וּ מִקְנֵיכֶ֔ם וְאֶתְּנָ֥ה לָכֶ֖ם בְּמִקְנֵיכֶ֑ם אִם־אָפֵ֖ס כָּֽסֶף׃
Da sprach Joseph: Bringt eure Herden, so will ich es euch für eure Herden geben, wenn ihr kein Geld mehr habt.
Haamek Davar on Genesis
If there is no more money. He did not believe them, so he told them to bring their livestock as a test, knowing they would rather part with money than their animals.