(6) باب الإِمْسَاكِ عَنِ الإِغَارَةِ، عَلَى قَوْمٍ فِي دَارِ الْكُفْرِ إِذَا سُمِعَ فِيهِمُ الأَذَانُ
Anas b. Malik reported:
The Messenger of Allah (ﷺ) used to attack the enemy when it was dawn. He would listen to the Adhan; so if he heard an Adhan, he stopped, otherwise made an attack. Once on hearing a man say: Allah is the Greatest, Allah is the Greatest, the Messenger of Allah (ﷺ) remarked: He is following al-Fitra (al-Islam). Then hearing him say: I testify that there is no god but Allah. there is no god but Allah, the Messenger of Allah (ﷺ) said: You have come out of the Fire (of Hell). They looked at him and found that he was a goat herd.
Reference: Sahih Muslim 382
In-book reference: Book 4, Hadith 11
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 745