Even if the only evidence we possessed were the fact that the Messenger of Allah, peace and blessings be upon him, deemed it lawful to shed the blood of people in whose territory no adhān is heard—along with taking their wealth and captives—that alone would suffice to show that giving the adhān is an obligatory duty. Ibn Ḥazm (3/125) made this very point, and he was alluding to the ḥadīth of Anas ibn Mālik (may Allah be pleased with him):

‘Whenever the Prophet, peace and blessings be upon him, attacked a people he would not launch a night raid until morning. If he heard the adhān he would hold back; if he did not hear the adhān he would assault them.’

Al-Bukhārī records this in the Book of the Adhān, and Aḥmad (3/159, 206, 236, 237) transmits it through several routes from Ḥumayd on Anas’s authority. Muslim (2/3–4), al-Tirmidhī (1/305, Būlāq edition)—who declared it sound—al-Dārimī (2/217), al-Ṭayālisī (271), and Aḥmad (3/132, 229) also narrate it through Ḥammād ibn Salamah → Thābit → Anas. All of them, except al-Dārimī and al-Ṭayālisī, add:

‘One day he listened attentively and heard a man saying, “Allāhu akbar, Allāhu akbar.” The Messenger of Allah said, “He is upon the fiṭrah (natural disposition).” Then the man said, “I bear witness that there is no god but Allah,” and the Prophet remarked, “He has been delivered from the Fire.”’ Muslim further adds: ‘They looked and saw that the man was a goatherd.’

This report is corroborated by his, peace and blessings be upon him, statement: ‘If you see a mosque or hear a caller, do not kill anyone.’ Al-Tirmidhī (1/292, Būlāq edition) and Aḥmad (3/448) relate it through the chain of Ibn ʿUyaynah → ʿAbd al-Malik ibn Nawfal ibn Masāḥiq → Ibn ʿIṣām al-Muzanī → his father—who was a Companion—who said: ‘Whenever the Messenger of Allah, peace and blessings be upon him, dispatched an army or a detachment he would say to them…’ and he mentioned the above words. Al-Tirmidhī said: