Musnad Abu Ya'la al-Mawsili 155:269

Narrated to us Mansur ibn Abi Muzahim, narrated to us Muhammad ibn Fudayl, from 'Amarah ibn al-Qa'qa', from Abu Zur'ah, from Abu Hurayrah, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) would say the Takbir in the prayer, he would remain silent between the Takbir and the recitation.