Should one complete Al-Fatiha if the Imam bows, or is it permissible not to complete it and bow with him?

Scholars have differed regarding the recitation of Al-Fatiha behind the Imam. The majority of scholars hold that the follower (ma'mum) should not recite Al-Fatiha or anything else behind the Imam in a loud prayer if he can hear the Imam's recitation. This is the view chosen by Shaykh al-Islam Ibn Taymiyyah and some verifying scholars.

The Shafi'is and those who agreed with them hold that it is obligatory for the follower to recite Al-Fatiha behind the Imam, whether in loud or silent prayers. This is the view upon which the fatwa (definition) is based. It is more precautionary for the follower to recite it to avoid the difference of opinion. Your prayer is valid as long as you did not find an opportunity to recite.