Dua at the start of the prayer (after takbeer)

لَبَّيْكَ وَسَعْدَيْكَ، وَالْخَيْرُ كُلُّهُ بِيَـدَيْكَ، وَالشَّـرُّ لَيْسَ إِلَيْـكَ، أَنَا بِكَ وَإِلَيْكَ، تَبَارَكْتَ وَتَعَالَيْتَ، أَسْتَغْفِرُكَ وَأَتُوبُ إِلَيْكَ

Transliteration

Labbayka wa sa'dayka, wal-khayru kulluhu biyadaika, washsharru laysa ilayka, anaa bika wa-ilayka, tabaarakta wa ta'Aalayta, astaghfiruka wa-atoobu ilayk

Meaning

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.

Source: Muslim: 771