Ruling on gesturing during prayer to return a greeting or answer a question

Q: What is the ruling on one who answers a questioner by nodding his head in affirmation or negation while he is in prayer? For example, if the questioner is in a hurry, he takes the answer from me while I am in prayer by asking, for instance, "Are you waiting for me?" and I answer him with my head, "Yes." Does this invalidate the prayer?
A: Praise be to Allah, Lord of the worlds, and the outcome is for the righteous, and may the prayer and peace be upon His servant and messenger, His choice from among His creation, and His trustee over His revelation, our Prophet, our Imam, and our Master Muhammad ibn Abdullah, and upon his family and his Companions, and whoever follows his path and is guided by his guidance until the Day of Judgment.
As for what follows: Gesturing during prayer is permissible, there is no blame in it, and it does not invalidate the prayer. The Prophet (peace and blessings be upon him), who is the master of creation and their teacher, did so, and his Companions (may Allah be pleased with them and grant them satisfaction) did so as well, so there is no blame in that. If a questioner asks you, "Are you waiting for me?" while you are in prayer, and you gesture with your head in a way that indicates agreement, there is nothing wrong with that. Or if a questioner asks about one of the rulings and you gesture in a way that indicates "yes" or "no," all of that is permissible. The Prophet (peace and blessings be upon him) did so, and he returned greetings by gesture, may the prayer and peace be upon him. And success is from Allah.