Yahya related to me from Malik that he had heard that a manquestioned al-Qasim ibn Muhammad saying, "My imagination works in theprayer, and it happens to me a lot." Al-Qasim ibn Muhammad said, "Goon with your prayer, for it will not go away from you until you go awaysaying, 'I have not completed my prayer.' "
App reference: Book 4, Hadith 3
USC-MSA web (English) reference: Book 4, Hadith 3
Arabic reference: Book 4, Hadith 225