Did not Abu Bakr Al-Siddiq know about the prohibition of Nikah Mut'ah, and if so, who informed Umar ibn Al-Khattab of its prohibition after a period of his caliphate?

Mut'ah marriage was forbidden in Islam by the Prophet Muhammad (peace be upon him). The prohibition by Umar ibn al-Khattab was not a personal ijtihad (definition) (independent reasoning), but rather an affirmation of the Prophet's prohibition, as some Companions continued to practice it due to their ignorance of its prohibition. Umar (may Allah be pleased with him) indicated in his sermon that the Prophet (peace be upon him) permitted mut'ah three times and then forbade it, and that mut'ah was forbidden until the Day of Judgment. Abu Bakr did not issue a ruling on it due to the brevity of his caliphate and his preoccupation with the Ridda (apostasy) wars.