اللّهُـمَّ إِنّـي أَعـوذُبِكَ أَنْ أُشْـرِكَ بِكَ وَأَنا أَعْـلَمْ، وَأَسْتَـغْفِرُكَ لِما لا أَعْـلَم
Allaahumma innee a oothu bika an ushrika bika wa anaa a lamu, wa astaghfiruka limaa laa a lamu.
O Allah, I seek refuge in You lest I associate anything with You knowingly, and I seek Your forgiveness for what I know not.
Ahmad 4/403. See also Al-Albani, Sahih ul-Jami As-Saghir 3/233 and Sahih ut-Targhib wat- Tarhib 1/19.