The testament of the Wilayat of Imam Ali (as) is not a part of
the Athaan nor Iqamah but is recited with the intention of nearness.
Thus if a person recites it with the intention that it is part of the
Athaan or Iqamah it becomes questionable. The reason for mentioning only
the name of Imam Ali (as) is that certain specialities belongs to Him
(as) alone. One of which is that He is the origination of Wilayat
(Imamah). Another reason is his distinguished status amongst the
Infallibles (as) that they themselves explained. There is no reliable
source about the time of introducing Imam Ali's (as) name in the Athaan.
What we can say is that the mentioning of Imam Ali's (as) name has been
a common practice for many centuries by Shia with the intention of
nearness, blessing and expressing their respect to the Master of the
Monotheist. Shia Scholars have not expressed their opposition to it.