From Sahih Bukhari (Hadith 7545):
Narrated `Aisha:(when the slanderers said what they said about her): I went to my bed knowing at that time that I was innocent and that Allah would reveal my innocence, but by Allah, I never thought that Allah would reveal in my favor a revelation which would be recited, for I considered myself too unimportant to be talked about by Allah in the Divine Revelation that was to be recited. So Allah revealed the ten Verses (of Surat-an-Nur). 'Those who brought a false charge
Reference: Bukhari 7545