What is the significance of the brothers' statement, "The money we found... we returned... how could we steal"?
Rashi: This is one of ten Kal va'Chomers in the Torah (including Nevi'im and Kesuvim). 1
Ohr ha'Chayim: The man had refuted this, through saying that sometimes thieves do nice acts (see 44:5:152). But they do not return 'consumed theft,' what was already taken and acquired far away! Rather, our return shows that we are honest.
Malbim: We returned it, even though (a) Kesef does not have a Siman; (b) we found it; (c) in our Amtachos - our Kelim acquired for us; (d) we returned it by ourselves (without being asked to); (e) from Eretz Kena'an - we were already in our Reshus. If so, how would we (a) steal (unlike a Metzi'ah), (b) from your master's house (unlike in our sacks), (c) [a Keli of] silver or gold, which has a Siman?!
All of which are listed in the Midrash Rabah (92:7).
Rashi said that the argument, "the money we had found... we returned..." is a Kal v'Chomer. Perhaps they returned it because they feared Yosef knew about the money through Nichush with his cup; and now they had stolen his cup!
Peninim mi'Shulchan ha'Gra: According to the opinion that permits Gezel Nochri, why must "Aveidas Achicha" (Devarim 22:3). exclude a Nochri's Aveidah? It must forbid returning it. Since we returned it, this shows that we forbid Gezel Nochri. All the more so we should not steal from you!
Why did they say "silver or gold"? They were accused of taking [the cup] with which Yosef drinks!
Ramban (to 44:5): They answered as if they had no idea what he was talking about.
Ohr ha'Chayim (to 44:7): You said that we returned the money so that people will trust us, to enable us to steal things worth more than what we returned. We do not do Nichush or [even] know how to. To, us, the cup is mere silver or gold (worth less than what we returned)! They said "or gold" to show that they do not even know from what is made the cup that he discusses.
