Sayyiduna Anas (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him), Sayyiduna Abu Bakr, and Sayyiduna Umar (may Allah be pleased with them both) used to begin recitation from «الحمد لله رب العالمين».
Hadith Referenceالمنتقى ابن الجارود / كتاب الصلاة / 182