Say ten times -

لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ، لَهُ الْمُلْكُ، وَلَهُ الْحَمْدُ، وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ

Laa 'ilaaha 'illAllahu wahdahu laa shareeka lahu, lahul-mulku wa lahul-hamdu wa Huwa 'alaa kulli shay'in Qadeer

None has the right to be worshipped except Allah, alone, without any partner. To Him belong all sovereignty and praise and He is over all things omnipotent. Whoever says this dua ten times is like one who has freed four slaves from among the children of Ismaa'eel.

Reference: Bukhari No: 6403; Muslim No: 2693