Someone who heard the Prophet ﷺ say it reported that he said, "Give every surah its due share of bowing and prostration."
حدثنا أبو معاوية وعبدة قالا ثنا عاصم
حدثني من سمع النبي ﷺ يقول أعطوا كل سورة حظها من الركوع والسجود
Its isnad is sahih. Haythami said, 2/114, "The narrators of Ahmad's version are the narrators of the Sahih." Bayhaqi also narrated it, 3/10, in the chapter on prayer.