In the first hadith, the words of the adhan (call to prayer) are nineteen, in which the words of the shahadatayn (the two testimonies) are recited four times each, and this is what is called tarji‘, that is, both statements of the shahadatayn are first recited twice in a low voice, and then again both statements of the shahadatayn are repeated twice in a loud voice.
This narration is authentic, and giving the adhan with tarji‘ in this manner is considered legislated (mashru‘) according to Imam Malik, Imam Shafi‘i rahimahumullah, and the majority of scholars. And in this narration, it is also established that the words of the iqamah (second call to prayer) are to be said twice each, without tarji‘, just like the adhan, and this action is not objectionable.