Brachos 8:7-8

Brachos 8:7

If a person ate but forgot to bentch, Bais Shammai says he must return to the place where he ate in order to recite bentching. Bais Hillel says he may bentch in the place where he realized he forgot. One may bentch until the food in his stomach is digested.

Brachos 8:8

If the diners were brought a cup of wine at the end of the meal and there’s no wine left after that, Bais Shammai says they may drink it even though that will leave no wine for bentching. Bais Hillel says the cup of wine must be saved for bentching. One says “amen” after hearing a Jew recite a bracha. One does not say “amen” after the blessing of a Samaritan unless he heard the entire bracha. (The Samaritans were quasi-Jewish and suspected of idolatry.)