Sa'id bin Jubayr narrates from Ibn Abbas (may Allah be pleased with them both) that the recitation should be begun with 'Bismillah al-Rahman al-Rahim' (In the name of Allah, the Most Gracious, the Most Merciful).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2405