It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet of Allah (peace and blessings be upon him) used to begin the prayer with 'Al-hamdu lillahi Rabbil-'alamin' (All praise is for Allah, Lord of the worlds).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12664