It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) entered the mosque, and then, in the complete hadith, he mentioned the story of the man who had entered the mosque. In it there is also that he (peace and blessings be upon him) said: "Then raise your head until you are standing perfectly straight."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2621