أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - هُوَ ابْنُ مَهْدِيٍّ - قَالَ حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ أَبِي سَلَمَةَ، قَالَ حَدَّثَنِي عَمِّي الْمَاجِشُونُ بْنُ أَبِي سَلَمَةَ، عَنْ عَبْدِ الرَّحْمَنِ الأَعْرَجِ، عَنْ عُبَيْدِ اللَّهِ بْنِ أَبِي رَافِعٍ، عَنْ عَلِيٍّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا سَجَدَ يَقُولُ ‏"‏ اللَّهُمَّ لَكَ سَجَدْتُ وَلَكَ أَسْلَمْتُ وَبِكَ آمَنْتُ سَجَدَ وَجْهِي لِلَّذِي خَلَقَهُ وَصَوَّرَهُ فَأَحْسَنَ صُورَتَهُ وَشَقَّ سَمْعَهُ وَبَصَرَهُ تَبَارَكَ اللَّهُ أَحْسَنُ الْخَالِقِينَ ‏"‏ ‏.‏

It was narrated from 'Ali that: When the Messenger of Allah (PBUH) prostrated he would say: "Allahumma laka sajadtu wa laka aslamtu wa bika amantu sajada wajhi lilladhi khalaqahu wa sawwarahu fa ahsana suratahu wa shaqqa sam'ahu wa basarahu, tabarak Allahu ahsanul-khaliqin ( O Allah, to You I have prostrated and to You I have submitted, and in You I have believed. My face has prostrated to the One Who created it and shaped it and shaped it well, and brought forth its hearing and sight. Blessed be Allah the best of Creators.)" Translation Not Available

Book reference: Sunan An Nisai Book 12 Hadith 1126
Web reference: Sunan An Nisai Volume 2 Book 12 Hadith 1127