He used to say the takbir every time he lowered himself and rose, and he would relate that the Messenger of Allah ﷺ used to do the same.
حدثنا قتيبة قال حدثنا يعقوب عن سهيل عن أبيه
أنه كان يكبر كلما خفض ورفع ويحدث أن رسول الله ﷺ كان يفعل ذلك
Its chain of transmission is sahih. Muslim narrated it in the Book of Prayer, chapter on affirming the takbir, 1/294, no. 392.