The Rambam (Rabbi Moshe Maimonides, 1135-1204) ruled that if a person ate a meal that requires Birkat Ha’mazon, but he forgot to recite Birkat Ha’mazon and then left the place where he ate, he may recite Birkat Ha’mazon in his new location. (This is assuming, of course, that he remembered to recite Birkat Ha’mazon within the period of time after eating that Birkat Ha’mazon may be recited.) Since this was done accidentally, the person does not have to return to the place where he ate for the recitation of Birkat Ha’mazon. However, if the person left knowing that he did not recite Birkat Ha’mazon, then he must return to where he ate and recite Birkat Ha’mazon at that location. Even in this case, however, if the person recited Birkat Ha’mazon in his new location, he has fulfilled the Misva, and does not have to then return to where he ate and repeat Birkat Ha’mazon.
The Rosh (Rabbenu Asher Ben Yehiel, 1250-1327), as well as his son, the Tur (Rabbenu Yaakob Ba’al Ha’turim, 1269-1343), ruled more stringently. In their view, even if this was done by mistake – meaning, one forgot to recite Birkat Ha’mazon before leaving – he must return to where he ate to recite Birkat Ha’mazon. The difference between intentionally and unintentionally leaving, according to this opinion, is that if one intentionally left without reciting Birkat Ha’mazon, then even Be’di’abad (after the fact), he cannot fulfill the requirement in his new location. One who mistakenly left must return for Birkat Ha’mazon, but if he did not, and recited Birkat Ha’mazon in his new location, he has fulfilled his obligation; one who knowingly left without reciting Birkat Ha’mazon, however, does not fulfill the Misva in his new location even after the fact. This is a very surprising opinion – that the intent of the person when he relocated can determine whether he fulfills the obligation if he recited Birkat Ha’mazon in his new location.
It is unclear which of these two positions was accepted by the Shulhan Aruch, who cites both views (in Orah Haim, 179). The Hid"a (Rav Haim Yosef David Azulai, 1724-1806) maintained that the Shulhan Aruch accepted the stringent position of the Rosh and Tur, and this is the ruling of the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Behaalotecha. However, Hacham Ovadia Yosef disagreed, and asserted that the Shulhan Aruch followed the lenient position of the Rambam.
In practice, the accepted view is that of the Rambam. And therefore, one who mistakenly left after a meal without reciting Birkat Ha’mazon may recite Birkat Ha’mazon in his new location. If one knowingly relocated without reciting Birkat Ha’mazon, he must return to where he ate for Birkat Ha’mazon, but after the fact, if he recited Birkat Ha’mazon in his new location, he has nevertheless fulfilled the obligation.
It must be noted, however, that both the Mishna Berura and Hacham Ovadia comment that even if one left mistakenly, it is preferable to return to where he ate for Birkat Ha’mazon, even though this is not strictly required. The Gemara tells the story of a person who returned to where he ate for Birkat Ha’mazon and he found a large sum of money there. This shows that under all circumstances, making a point of returning to the place where one ate for the recitation of Birkat Ha’mazon is admirable and brings blessing.
Additionally, in the case of a person who knowingly left without reciting Birkat Ha’mazon, who is required to return to where he ate, he may recite Birkat Ha’mazon in his new location if he would otherwise forfeit the Misva. Meaning, if the time in which he may recite Birkat Ha’mazon (generally assumed to be 72 minutes after eating) would pass if he returns to his original location, then he should recite Birkat Ha’mazon in his current location. Moreover, under extenuating circumstances, such as if he would miss a flight if he returns to his original location, then he should recite Birkat Ha’mazon where he is currently.
These Halachot clearly underscore for us the importance of ensuring to recite Birkat Ha’mazon after completing one’s meal before leaving, and care must be taken not to leave before fulfilling this precious Misva.
Summary: One should not leave after eating a meal before reciting Birkat Ha’mazon. If one forgot to recite Birkat Ha’mazon before leaving, and he left, he may recite Birkat Ha’mazon in his new location, though it is preferable to return to where he ate. If he knowingly left without reciting Birkat Ha’mazon, then he must return to where he ate for the recitation of Birkat Ha’mazon, unless this would cause him to miss the deadline for reciting Birkat Ha’mazon, or would cause great inconvenience, such as missing a flight.
