Is the Adhan of the Sunnis incomplete, and what are its legal forms?

The Sunnis rely in their adhan on what was authentically reported from the Prophet, peace and blessings be upon him, in the hadiths of Abdullah ibn Zayd and Abu Mahdhurah, may Allah be pleased with them both.

The adhan of Abdullah ibn Zayd consists of fifteen phrases, and it was adopted by Abu Hanifa and Ahmad. It is: "Allahu Akbar (4 times), Ashhadu an la ilaha illa Allah (2 times), Ashhadu anna Muhammadan Rasoolullah (2 times), Hayya 'ala as-Salah (2 times), Hayya 'ala al-Falah (2 times), Allahu Akbar (2 times), La ilaha illa Allah."

The adhan of Abu Mahdhurah consists of seventeen phrases, with the takbir (Allahu Akbar) said twice at the beginning, along with the tarji' (repeating the Shahadahs quietly then loudly). This was adopted by Malik.

Ash-Shafi'i also adopted the adhan of Abu Mahdhurah, but he made the takbir at the beginning four times. It is: "Allahu Akbar (4 times), Ashhadu an la ilaha illa Allah (2 times), Ashhadu anna Muhammadan Rasoolullah (2 times), then the Shahadahs are repeated with a raised voice, Hayya 'ala as-Salah (2 times), Hayya 'ala al-Falah (2 times). If it is the Fajr prayer, you say: As-Salatu Khayrun min an-Nawm (2 times), Allahu Akbar (2 times), La ilaha illa Allah."

Everything that has come from the Sunnah is true, and there is no harm in calling the adhan with it. It is desirable to use all of them, sometimes this and sometimes that, as long as it does not cause disagreement or discord.