اَللَّهُمَّ لَا طَيْرَ إِلاَّ طَيْرُكَ، وَلَا خَيْرَ إِلَّا خَيْرُكَ، وَلَا إِلَهَ غَيْرُكَ

Allaahumma laa tayra illaa tayruka, wa laa khayra illaa khayruka, wa laa ilaaha ghayruk

O Allah, there is no omen but there is reliance on You, there is no good except Your good and none has the right to be worshipped except You. Ibn 'Umar (RA) said: The Messenger of Allah (ﷺ) said: The Companions said, O Messenger of Allah, what is the expiation for such a thought? He said he should say (the above words).

Reference: Sahih (Albani). Silsila Sahiha: 1065, Musnad Ahmad: 7045