It was narrated from Abu Sa'eed Al-Khudri that the Messenger of Allah (ﷺ) said:
"When you hear the call, say what the Mu'adhdhin says." (RU)
English reference (RU): Vol. 1, Book 7, Hadith 674 (RU)
Arabic reference (RU): Book 7, Hadith 681 (RU)