Musnad Ahmad 1156:111

Yahya ibn Sa'id al-Umawi narrated to us, he said: Ibn Jurayj narrated to us, from 'Abdullah ibn Abi Mulaykah, from Umm Salamah, that she was asked about the recitation of the Messenger of Allah, may Allah bless him and grant him peace, and she said: "He used to pause in his recitation, verse by verse: 'In the name of Allah, the Entirely Merciful, the Especially Merciful,' 'All praise is due to Allah, Lord of the worlds,' 'The Entirely Merciful, the Especially Merciful,' 'Sovereign of the Day of Recompense.'"