Wa alaikum salam, In fajr, there are two Adhans! People usually use one adhan to  indicate the break of dawn which tells people it is time to pray and  also time to retain from eating and drinking. People must refrain from eating once this Adhan begins and not  continue to the end of it!

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Wa alaikum salaam This is recommended in prayers such as: Fajr, Maghreeb and Isha. Rather than that it should be silent, however this is not obligatory.

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