Thus it appears in Ṣaḥīḥ Muslim: “Allāhu akbar, Allāhu akbar” only twice.

Al-Nasāʾī likewise recorded it (1/103): Isḥāq b. Ibrāhīm informed us, he said, “Muʿādh b. Hishām narrated it to us,” but he mentioned the opening takbīr four times.

This Isḥāq is one of Muslim’s two teachers for this ḥadīth; the other is Abū Ghassān al-Mismaʿī, Mālik b. ʿAbd al-Wāḥid. It is probably the latter who transmitted it with the takbīr said twice, whereas Isḥāq related it with the takbīr said four times, as found in al-Nasāʾī.

Abū Nuʿaym related the report in his Mustakhraj, and al-Bayhaqī as well, through the route of Isḥāq b. Ibrāhīm from Muʿādh b. Hishām with his chain, and in it the takbīr is quadrupled.
Abū ʿAwānah also produced it in his Mustakhraj through ʿAlī b. al-Madīnī from Muʿādh.

For that reason Ibn al-Qaṭṭān said: “What is sound here is that the takbīr is recited four times; on that basis the adhān consists of nineteen phrases, and this is explicitly stated within the very ḥadīth. He added: it does occur in some narrations of Muslim with four takbīrs, and those are the versions that should be counted as authentic.” End of quotation from al-Talkhīṣ (3/160).

The ḥadīth has yet another line of transmission from Ibn Muḥayriz. Ibn Jurayj narrated: ʿAbd al-ʿAzīz b. ʿAbd al-Malik b. Abī Maḥdhūrah told me that ʿAbdullāh b. Muḥayriz informed him—he had been an orphan under the guardianship of Abū Maḥdhūrah when the latter outfitted him for al-Shām—saying: “I said to Abū Maḥdhūrah, ‘I am leaving for al-Shām and I fear I may be asked about the way you call to prayer.’ So he told me that Abū Maḥdhūrah said to him…”