What is the origin of reciting Al-Fatiha after the the Adhan in mosques?

There is no basis for reciting Al-Fatihah in mosques after the Adhan (call to prayer). This is impermissible for the muezzin or anyone else, because the fundamental principle in acts of worship is tawqif (restriction to what is prescribed), and any addition not mentioned in the Sunnah is considered rejected, according to the words of the Prophet (peace be upon him): "Whoever introduces into this matter of ours that which is not from it, it is rejected." It is obligatory to adhere to the Sunnah of the Prophet (peace be upon him) and not to innovate what he or his Companions did not do, for every innovation is misguidance. Al-Hafiz Ibn Kathir said: "Every action and saying that is not proven from the Companions (may Allah be pleased with them) is an innovation; because if it were good, they would have preceded us to it."