أَعـوذُ بِاللهِ مِنَ الشَّيْـطانِ الرَّجيـم
aAAoothu billahi minash-shaytanir-rajeem
Translation
I take refuge with Allah from the accursed devil.
When to recite
Said when yawning. One should try to suppress the yawn by covering one's mouth with the hand.
Source / Reference
Al-Bukhari 10/505, Muslim 4/2293