Can’t recall part of a verse during prayer

If the Imam recited a part of the Qur’an and forgot the ending of the verse, and none of the followers reminded him of it, he can choose either to say the takbeer and discontinue the recitation, or recite a verse or more from another surah. But this is allowed only if the forgotten part is not from Al-Fatihah. As far as Al-Fatihah is concerned, it must be recited in its entirety as reciting it is an obligatory act of prayer.¹