Where does it say that if one (who is eating alone) wishes to leave in the middle of a seudah (even if they will return after some time -- however before the time that is allowed for them to make an after bracha has passed) they must first make an after bracha (particularly by bircas hamazon, although perhaps other brachas as well?) This has been something that I always heard was the "right" thing to do? Does it have a source?
In a previous question it was discussed what to do if someone did leave and then came back to their seudah if they may continue eating or if they need to make an after bracha first and then a new bracha. My question is where does it say (in poskim) that a person must make an after bracha before leaving.