Abu Musa Ashari reported,
When the Messenger of Allah ﷺ set out to fight at Khaybar, or he said, when the Messenger of Allah ﷺ set out, the people came in sight of a valley and raised their voices with the takbir, "Allah is the Greatest, Allah is the Greatest, there is no god but Allah."The Messenger of Allah ﷺ said, "Go easy on yourselves. You are not calling upon one who is deaf or absent. You are calling upon one who hears and is near, and He is with you."
Azami 329
Sahihعن أبي موسى الأشعري قال
لما غزا رسول الله ﷺ خيبر أو قال: لما توجه رسول الله ﷺ أشرف الناس على واد فرفعوا أصواتهم بالتكبير: الله أكبر الله أكبر، لا إله إلا الله. فقال رسول الله ﷺ: اربعوا على أنفسكم، إنكم لا تدعون أصم ولا غائبا، إنكم تدعون سميعا قريبا وهو معكم.
Bukhari narrated it in the Book of Military Expeditions (4205), and Muslim in the Book of Remembrance (2704), both from the hadith of Asim, from Abu Uthman, from Abu Musa, who related the hadith, and this is a part of it. Bukhari also narrated it in the Book of Supplications (6384), and Muslim as well, both from the hadith of Hammad bin Zayd, from Ayub, from Abu Uthman, from Abu Musa, who related the hadith, but in Bukhari's version it came with the wording, "but you are calling upon one who hears and sees." The hadith has other chains of transmission and additional wording.