Asmaa’ bint ‘Umays said: "The Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said to me: ‘Shall I not teach you some words to say at times of distress? "O Allaah, You are my Lord and I do not associate anything with You."’" (Reported by Abu Dawud in al-Sunan, Kitaab al-salaat, Baab fi’l-istighfaar; see also Saheeh al-Jaami‘, no. 2623).