Why do the Imams begin reciting Surat Al-Fatihah aloud in prayer with "Alhamdulillah Rabb Al-Alamin (All praise is due to Allah, Lord of the worlds)," even though the first verse in it is "Bismillahir Rahmanir Rahim (In the name of Allah, the Most Gracious, the Most Merciful)"?

It appears that the imams recite the Basmalah silently. The abandonment of reciting it aloud in audible prayers is a well-known Sunnah from the Prophet, peace and blessings be upon him, as stated in the Hadith of Anas: "They used to begin the prayer with 'Alhamdulillah Rabbil-Alamin (All praise is due to Allah, Lord of the Worlds).'" Muslim added: "They would not mention 'Bismillahir-Rahmanir-Rahim (In the name of Allah, the Most Gracious, the Most Merciful)' at the beginning of the recitation nor at its end." The disagreement regarding whether the Basmalah is a verse of Al-Fatiha is ancient. Sheikh al-Islam Ibn Taymiyyah preferred the view that it is not part of it, based on the Hadith: "I have divided the prayer between Myself and My servant into two halves."