سنن النسائي

It was narrated from Abdul-Jabbar bin Wa'il that his father said: "I prayed behind the Messenger of Allah (ﷺ) and when he started to pray he said the Takbir and raised his hands until they were in level with his ears. Then he recited the Opening of the Book, and when he had finished he said 'Amin' and raised his voice with it."