Say three times:

رَضِيتُ بِاللَّهِ رَبًّا، وَبِالْإِسْلاَمِ دِينًا وَبِمُحَمَّدٍ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ نَبِيًّا

I am pleased with Allaah as a Lord, and Islaam as a religion and Muhammad as a Prophet.

Radheetu billaahi Rabban, wa bil-'Islaami deenan, wa bi-Muhammadin (sallallaahu 'alayhi wa sallama) Nabiyyan.

Allah has promised that anyone who says every morning or evening will be pleased on the Day of Resurrection.

Ahmad 4/ 337, An-Nasa'i, Ibn As-Sunni (no. 68), At-Tirmizi 5/465.