Ate Bread and Don't Remember if Birkat Hamazon Was Recited
Question
Answer
If you can eat more bread, wash your hands and recite the first blessing over it (due to distraction). If you cannot eat more, if you ate the amount that satisfies, recite the blessing. If you did not eat the amount that satisfies, do not recite the blessing.
Source
Mishnah Berurah, Siman 184, Subparagraph 15. This is because the obligation of Birkat Hamazon is from the Torah, as it is written: 'And you shall eat and be satisfied, and bless.' The early authorities disagreed whether the Torah obligation is for an olive-sized amount or an amount that satisfies. Therefore, if not satisfied, do not recite the blessing due to a double doubt: doubt whether the blessing was recited, and doubt whether the obligation is from the Torah. See there in Biur Halacha, in the section 'If.'