Ruling on saying, “O you (Muhammad), the first of the creation” before or after Athaan

Question 458: After Athaan (call to Prayer), some people say, “O you the first of Creation” although the Messenger of Allaah is not the first human created by Allaah (Exalted be He). Is this permissible?

Answer: It is not permissible to say any form of thikr (Remembrance of Allaah) out loud before or after Athaan. It is obligatory to confine the Athaan to that which was legislated by Allaah (Exalted be He). Whoever adds anything to it is Mubbtadi` (one who introduces innovations in religion). The Prophet (peace be upon him) said: Anyone who does an action which is not stated in this matter of ours (Islaam) will have it rejected. And, “Avoid novelties (in religion), for every novelty is an innovation.” What is mentioned in the question is invalid, as the Messenger of Allaah (peace be upon him) is not the first human created by Allaah (Exalted be He). This is false and it involves exceeding the proper limits in honouring him (peace be upon him). The Prophet (peace be upon him) said: “Do not exaggerate in praising me as the Christians praised the son of Mary, for I am only a Slave. So, call me the Slave of Allaah and His Messenger.” more here.