Musnad Ahmad 658:229

Abu Kamil narrated to us, Sharik narrated to us, from Abu Ishaq, from Al-Bara’ ibn ‘Azib, that he described the prostration (sujud) and said: He spread his palms, raised his buttocks, and kept his arms away from his sides (ta-khawa). And he said: "This is how the Prophet, may Allah bless him and grant him peace, prostrated."