It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you bows and says 'Subhana rabbiyal-'azim' (Glory be to my Lord, the Most Great) three times, his bowing is complete, and this is its minimum. When one of you prostrates and says 'Subhana rabbiyal-a'la' (Glory be to my Lord, the Most High) three times, his prostration is complete, and indeed this is its minimum."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2689
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