Sahih Al Bukhari (480)

عن أبي هريرة {أن رسول الله صلى الله عليه وسلم قال إذا نودي للصلاة أدبر الشيطان وله ضراط حتى لا يسمع التأذين فإذا قضى النداء أقبل حتى إذا ثوب بالصلاة أدبر حتى إذا قضى التثويب أقبل حتى يخطر بين المرء ونفسه يقول اذكر كذا اذكر كذا لما لم يكن يذكر حتى يظل الرجل لا يدري كم صلى}

Abu Hurayrah (may Allah be pleased with him) narrated that Allah’s Messenger (peace be upon him) said: "When the Adhan is pronounced Satan takes to his heels and passes wind with noise during his flight in order not to hear the Adhan. When the Adhan is completed, he comes back and again takes to his heels when the Iqamah is pronounced and after its completion he returns again till he whispers into the heart of the person (to divert his attention from his Salah) and makes him remember things which he does not recall to his mind before Salah and that causes him to forget how much he has prayed.”