Ata bin Yazid reported that Abu Saeed Khudri said, "The Messenger of Allah ﷺ said, 'When you hear the call to prayer, repeat what the caller says.'"
قال عبد الله حدثناه عبد الله بن عون الخراز ومصعب الزبيري قالا حدثنا مالك بن أنس عن الزهري فذكر مثله سواء
Its isnad is sahih, and Ata bin Yazid Laythi is trustworthy. The second route is among the additions of Abdullah, and the hadith appears at greater length in the Sahihayn. Bukhari related it, 1/159, in the chapter on the adhan, what one says upon hearing the caller. Muslim related it, 1/288, no. 383. Abu Dawud related it, 1/144, no. 522. Tirmidhi related it, 1/407, no. 208, and said, hasan sahih. And Nasai related it, 2/23, in the chapter on the adhan, saying the same as the muezzin says, Sabih edition.