ENOfficial
Islam al-Muzani said: God’s Messenger sent us in a detachment and said, “When you see a mosque or hear a mu’adhdhin (The one who makes the call to prayer) do not kill anyone.” Tirmidhi and Abu Dawud transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَن عصامٍ المزنيِّ قَالَ بَعَثَنَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي سَرِيَّةٍ فَقَالَ: «إِذَا رَأَيْتُمْ مَسْجِدًا أَوْ سَمِعْتُمْ مُؤَذِّنًا فَلَا تَقْتُلُوا أَحَدًا» . رَوَاهُ التِّرْمِذِيّ وَأَبُو دَاوُد
sunnah.com