וְאֶת־גְּבִיעִ֞י גְּבִ֣יעַ הַכֶּ֗סֶף תָּשִׂים֙ בְּפִי֙ אַמְתַּ֣חַת הַקָּטֹ֔ן וְאֵ֖ת כֶּ֣סֶף שִׁבְר֑וֹ וַיַּ֕עַשׂ כִּדְבַ֥ר יוֹסֵ֖ף אֲשֶׁ֥ר דִּבֵּֽר׃
Y pondrás mi copa, la copa de plata, en la boca del costal del menor, con el dinero de su trigo. Y él hizo como dijo José.
Rashi on Genesis
גביעי MY CUP — a long goblet called maderin in old French.
Sforno on Genesis
תשים בפי אמתחת הקטן, in order to test how the brothers would react to Binyamin becoming involved as the victim of a potentially life-threatening accusation, and what the brothers would do in order to save him.
Siftei Chakhamim
גביע is a tall goblet... Since it is written גביע twice, Rashi deduced that it means a tall cup. We need not ask: Why was Yoseif not concerned they would [later] claim the goblet was theirs? Because [the answer is:] It was for divination, so surely it was [not theirs but] Yoseif’s. For it says, “There is no divination amongst Yaakov” (Bamidbar 23:23). (author’s commentary)