Sa'id al-Jurayri narrates from a man of Banu Tamim, whom he praised highly, the narration of his father (may Allah be pleased with him), that he said: I prayed behind the Messenger of Allah (peace and blessings be upon him). The narrator says: I asked about the length of the bowing and prostrations of the Messenger of Allah (peace and blessings be upon him), and he said: He (peace and blessings be upon him) would remain as long as it takes a person to say 'Subhanallahi wa bihamdihi' (Glory be to Allah and with His praise) three times.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2690