The Messenger of Allah ﷺ said, "Allah forgives the caller to prayer for the full extent of his voice, and every moist and dry thing that hears his voice bears witness for him."
حدثنا أبو الجواب حدثنا عمار بن رزيق عن الأعمش عن مجاهد
قال رسول الله ﷺ يغفر الله للمؤذن مد صوته ويشهد له كل رطب ويابس سمع صوته
Its isnad is sahih. Abu Jawab Dabbi is Ahwas bin Jawab, whose reliability was established earlier at 2883. Haythami mentioned the hadith in Majma al-Zawaid 1:325-326, and said, "Ahmad, Tabarani in Al-Kabir, and Bazzar reported it... and its narrators are the narrators of the sahih." Munziri likewise mentioned it in Targhib wal-Tarhib 1:107 and said, "Ahmad reported it with a sahih isnad, and Tabarani in Al-Kabir and Bazzar also reported it." It is remarkable that Munziri and Haythami mentioned it using the wording of the narration that follows this one, in whose isnad there is an unnamed man, and there is a degree of laxity in this, even though the narration is sahih given that the unnamed man in its isnad is known from this narration to be Mujahid.As for his saying, "the extent of his voice," Ibn Athir said, "Al-madd means the measure, meaning the measure of sins. That is, he is forgiven up to the full extent of his voice." This is a figure of speech expressing the vastness of forgiveness, like the saying of another, "If you met me with sins filling the extent of the earth, I would meet you with forgiveness for them." It is also transmitted as "the extent of his voice" in another wording, and this will come up again, referring to the hadith of Abu Hurairah that follows at 7600.