Mukhtasar Muslim

Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) would attack the enemy early in the morning and would listen attentively for the sound of the adhan. If he heard the sound of the adhan (from the opponents’ city), he would not attack them. Once, he heard a man saying "Allahu Akbar, Allahu Akbar," so he said, "He is a Muslim." After that, he heard him say, "Ashhadu an la ilaha illallah, ashhadu an la ilaha illallah," so he said, "O man, you have been saved from the Fire." When people looked, he was a shepherd of goats.

It is narrated from Sayyiduna Abu Huraira, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: When the call to prayer (adhan) is given, Satan turns his back and flees while passing wind so that he does not hear the adhan. After the adhan, he returns, and when the iqamah (second call to prayer) is pronounced, he again flees. After the iqamah, he comes back and puts whispers into a person's heart and reminds him of things which he had not even thought of before the prayer, so much so that the person does not remember how many rak‘ahs he has prayed.