What is the ruling regarding a congregant who forgot to recite Al-Fatihah in one of the rak'ahs and did not remember until after the Imam bowed: should he make up a rak'ah, or does the Imam bear it on his behalf?

If the Imam forgets the Fatiha in a rak'ah, he must perform a replacement rak'ah. As for the congregant (ma'mum), he should not follow the Imam if the latter stands for an additional rak'ah, whether the congregant thinks it is an extra rak'ah or knows it is because the Imam omitted the Fatiha. Instead, the congregant should wait for the Imam and make the salām with him, or intend to separate from him and make the salām alone. However, a congregant forgetting the Fatiha does not harm his prayer according to the majority of scholars, because the Imam bears the responsibility of the recitation on his behalf. According to the Shafi'i school, if a congregant forgets the Fatiha until he bows (rukū'), he must perform a replacement rak'ah.