Shulchan Arukh Orach Chayim · Siman 192

English

The blessing of zimun (the invitation to recite Birkat HaMazon) with three or ten participants. This siman contains two se'ifim. If three were reclining together for a meal, they are obligated in zimun. One of them says, ‘Let us bless Him of whose bounty we have eaten,’ and they respond, ‘Blessed is He of whose bounty we have eaten and through whose goodness we live.’ He then repeats, ‘Blessed is He of whose bounty we have eaten and through whose goodness we live. Blessed are You, Hashem our God, King of the universe, who nourishes the world,’ etc. If there are four, he may say, ‘Bless Him of whose bounty we have eaten,’ but it is better to say, ‘Let us bless,’ so as not to exclude himself from the group. If there are ten, he must mention God, saying, ‘Let us bless our God,’ etc., and they respond, ‘Blessed is our God,’ etc. One must not say ‘Let us bless to our God’—le-Eloheinu, with a lamed. Whether there are ten, a hundred, a thousand, or ten thousand, they recite the blessing in this same manner. Anyone who changes this wording—for example, saying, ‘Let us bless for the food we have eaten,’ or saying ‘to the One of whose bounty we have eaten’ (le-mi she-achalnu mishelo), or saying ‘from His goodness’ (mi-tuvo) instead of ‘through His goodness’ (u-vetuvo), or saying ‘are alive’ (chayim) instead of ‘we live’ (chayinu)—is unlearned. When there are ten, however, since they mention the Name, he may say, ‘Let us bless our God for the food we have eaten of His bounty.’

English

If, in a group of ten, the leader of the zimun and those responding erred and did not mention ‘our God,’ they may not repeat it. But if they have not yet responded to him, he should repeat the zimun with the Name.