Dua when feeling that something is a bad omen
اللَّهُمَّ لَا طَيْرَ إِلَّا طَيْرُكَ ، وَلَا خَيْرَ إِلَّا خَيْرُكَ ، وَلَا إِلَهَ غَيْرُكَ
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.
Note: This supplication is used whenever one initially thinks a casual event or occurrence to foretell good or evil, using it as a basis to determine which action he should undertake, but he then denounces such a link, relies on Allah and then says this supplication as an expiation for this act, since it falls under the category of shirk.
allaahumma laa ṭayra illaa ṭayruka, wa laa khayra illaa khayruka, wa laa ilaaha ghayruk
Sources: Ahmad No# 7045; Ibn As-Sunni #292.