Reference : Hisn al-Muslim 29

وَجَّهـتُ وَجْهِـيَ لِلَّذي فَطَرَ السَّمـواتِ وَالأَرْضَ
حَنـيفَاً وَمـا أَنا مِنَ المشْرِكين ،
إِنَّ صَلاتـي ، وَنُسُكي ، وَمَحْـيايَ ، وَمَماتـي للهِ رَبِّ العالَمين ،
لا شَريـكَ لَهُ وَبِذلكَ أُمِرْتُ وَأَنا مِنَ المسْلِـمين.
اللّهُـمَّ أَنْتَ المَلِكُ لا إِلهَ إِلاّ أَنْت،
أَنْتَ رَبِّـي وَأَنـا عَبْـدُك ،
ظَلَمْـتُ نَفْسـي وَاعْـتَرَفْتُ بِذَنْبـي 
فَاغْفِرْ لي ذُنوبي جَميعاً
إِنَّـه لا يَغْـفِرُ الذُّنـوبَ إلاّ أَنْت.
وَاهْدِنـي لأَحْسَنِ الأَخْلاقِ 
لا يَهْـدي لأَحْسَـنِها إِلاّ أَنْـت ،
وَاصْـرِف عَـنّْي سَيِّئَهـا، 
لا يَصْرِفُ عَـنّْي سَيِّئَهـا إِلاّ أَنْـت،
لَبَّـيْكَ وَسَعْـدَيْك، 
وَالخَـيْرُ كُلُّـهُ بِيَـدَيْـك،
وَالشَّرُّ لَيْـسَ إِلَـيْك ، 
أَنا بِكَ وَإِلَيْـك ، 
تَبـارَكْتَ وَتَعـالَيتَ 
أَسْتَغْـفِرُكَ وَأَتوبُ إِلَـيك
Wajjahtu wajhiya li 'l-ladhî faṭara s-samāwāti wa 'l-arḍa, 
ḥanīfan wa mā ana min al-mushrikīna. 
Inna salāti wa nusukī, wa mahyāya wa mamātī lillāhi rabbi 'l-`ālamīna,
lā sharīka lahu. Wa bi dhālika umirtu wa ana min al-muslimīna. 
Allāhumma anta 'l-maliku lā ilāha illā anta.
Anta rabbī wa ana `abduka, 
ẓalamtu nafsī wa`taraftu bi dhanbī. 
Faghfir lī dhunūbī jamī`an, 
innahu lā yaghfiru 'dh-dhunūba illā anta. 
Wahdinī li-aḥsani 'l-akhlāqi, 
lā yahdī li aḥsanihā illā anta. 
Waṣrif `annī sayyi'ahā, 
lā yaṣrifu `annī sayyi'ahā illā anta. 
Labbayka wa sa`dayka, 
wa 'l-khayru kulluhu bi yadayka, 
wa 'sh-sharru laysa ilayka, 
ana bika wa ilayka, 
tabārakta wa ta`ālayta, 
astaghfiruka wa atūbu ilayka.

"I have turned my face sincerely towards He who has brought forth the heavens and the Earth 
and I am not of those who associate (others with Allah). 
Indeed my prayer, my sacrifice, my life and my death are for Allah, Lord of the worlds,
no partner has He, with this I am commanded and I am of the Muslims. 
O Allah, You are the Sovereign, none has the right to be worshipped except You. 
You are my Lord and I am Your servant, 
I have wronged my own soul and have acknowledged my sin, 
so forgive me all my sins 
for no one forgives sins except You. 
Guide me to the best of characters 
for none can guide to it other than You, 
and deliver me from the worst of characters 
for none can deliver me from it other than You. 
Here I am, in answer to Your call, happy to serve you. 
All good is within Your hands 
and evil does not stem from You. 
I exist by your will and will return to you. 
Blessed and High are You, 
I seek Your forgiveness and repent unto You."

Reference:
Muslim 1/534

Chapter: At the start of the prayer (after takbeer)