Is it a condition to adhere to a specific wording when uttering the Two Testimonies (Shahadatayn), or is there flexibility in the matter, and is it sufficient to say: "There is no god but Allah, Muhammad is the Messenger of Allah" to enter Islam, and is it considered correct to utter it with the addition of the word "His servant"?

It is prescribed to pronounce the two words of Tawhid (Oneness of God) together: "I bear witness that there is no god but Allah, and I bear witness that Muhammad is the Messenger of Allah." By uttering these, a person becomes a Muslim, provided that this is accompanied by firm belief and action. The permissibility of adding the word "His servant" for the Messenger of Allah has been mentioned in several authentic hadiths. Scholars have differed regarding a disbeliever's entry into Islam: whether it is required for them to pronounce both testimonies together, or if it suffices to pronounce the testimony "there is no god but Allah" and then be asked to testify to the prophethood. Some scholars hold the view that a disbeliever should be taught both testimonies together because they do not become a Muslim except by both of them.