It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) prayed, he would raise his gaze towards the sky. Then this verse was revealed: "Those who humble themselves in their prayers" [Surah al-Mu'minun: 2], so he (peace and blessings be upon him) lowered his blessed head.
Hammad bin Zayd narrated it from Ayyub as a mursal report, and this is what is preserved.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3542