It was narrated from Abu Sa’ib that he heard Abu Hurairah say:“The Messenger of Allah (ﷺ) said: ‘Whoever performs a prayer in which he does not recite Ummul Qur’an (the Mother of the Qur’an, i.e., Al- Fatihah), it is deficient; not complete.’” I said: ‘O Abu Hurairah, sometimes I am behind the Imam. He pressed my forearm and said: ‘O Persian! Recite it to yourself.’”

English translation · Sunan Ibn Majah