It is narrated from al-Sha'bi (may Allah have mercy on him): I saw Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) and also prayed behind him. He (may Allah be pleased with him) used to recite 'In the name of Allah, the Most Gracious, the Most Merciful' [Surah al-Fatihah: 1] aloud.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2401