In relation to adding the phrase: ” And I bear witness that ‘Isa (Jesus) is Allah’s Slave and His Messenger” to the Two Testimonies of Faith when dictating the Shahaadah to a Christian who is embracing Islam, then it is something discussed by the Scholars. A group of the Scholars hold the opinion that if a Christian is accepting Islam, then it is necessary to dictate to him the above phrase alongside the Shahaadah. They use as proof the Hadith of Ubadah bin Saamit (may Allah be pleased with him) that the Prophet (ﷺ) said:
مَنْ شَهِدَ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ، وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ، وَأَنَّ عِيسَى عَبْدُ اللَّهِ وَرَسُولُهُ وَكَلِمَتُهُ، أَلْقَاهَا إِلَى مَرْيَمَ، وَرُوحٌ مِنْهُ، وَالْجَنَّةُ حَقٌّ وَالنَّارُ حَقٌّ، أَدْخَلَهُ اللَّهُ الْجَنَّةَ عَلَى مَا كَانَ مِنَ الْعَمَلِ
If anyone testifies that None has the right to be worshipped in truth except Allah Alone Who has no partners, and that Muhammad is His Slave and His Messenger, and that Jesus is Allah’s Slave and His Messenger and His Word which He bestowed on Mary and a Spirit created by Him, and that Paradise is true, and Hell is true, Allah will admit him into Paradise with the deeds which he had done even if those deeds were few [al-Bukhari (no. 3435) and Muslim (no. 28)]
In explanation of this Hadith, Abul-‘Abbas al-Qurturbi (d. 656 H.)-may Allah have mercy upon him-said: “That which is taken/benefited from this Hadith is what to dictate to a Christian when he is accepting Islam” [al-Mufhim (1/200)]
Hafidh Ibn Hajar (d. 852 H.)-may Allah have mercy upon him-mentioned the same from al-Qurtubi [Fath ul-Baari (2/546)]
The reasoning behind this is that when a Christian or Jew accepts Islam, they need to free themselves from their previous Religion by professing clearly the truth they are accepting. So in the case of the Christians, they believe ‘Isa (Jesus) is the son of God and that he is divine, so in their testimony of faith they need to free themselves from this belief by affirming that he is a servant of Allah and His Messenger [See: Badaa’i as-Sanaa’i (7/103), Fath ul-Qadeer (6/70), and al-Mowsoo’ah al-Fiqhiyyah (4/268)]
With that, some of our contemporary Scholars say it is necessary that a Christian add the above phrase to their Shahaadah.
Shaikh Salih al-Fawzaan (may Allah preserve him) was asked:
Question: “Is it necessary for a Christian, when he is entering into Islam, to bear witness that ‘Isa (Jesus) is the servant of Allah and His Messenger, alongside the Shahaadatayn?
Answer: “It is necessary. It is necessary that he acknowledges that ‘Isa is the servant of Allah and His Messenger so that he does not combine between Islam and Christianity” [https://www.youtube.com/watch?v=zOTtjp-0jkc]
This is also the view of Shaikh Abdul-Kareem al-Khudayr (may Allah preserve him) [https://shkhudheir.com/scientific-lesson/673350751]
However, what seems to be correct is that it is not obligatory that a Christian have to utter this phrase along with the Shahaadah in order to enter Islam as long as they believe that ‘Isa (Jesus) is the servant of Allah and His Messenger. If they pronounce the Shahaadah, then they are Muslim.
Shaikh Bin Baz (d. 1420 H.)-may Allah have mercy upon him-was asked:
Question: May Allah bless you, O Shaikh. There is the Hadith: “And I bear witness that ‘Isa (Jesus) is Allah’s Slave and His Messenger and His Word which He bestowed on Mary and a Spirit created by Him”. Some people obligate a Christian to pronounce that ‘Isa is the servant of Allah and His Messenger alongside the Shahaadah when they are accepting Islam?
Answer: “It is necessary that he affirm that. It is necessary that he affirm that and believe this. That he believe that ‘Isa is the servant of Allah and His Messenger, and that he is not the son of God, and he is not Allah and he is not the third of the three (i.e. in the Trinity) . . .” [Binbaz.site]
Shaikh Abdul-Muhsin al-‘Abbad (may Allah preserve him) was asked:
Question: If a Christian accepts Islam is it necessary to request him to bear witness that ‘Isa (Jesus) is the servant of Allah and His Messenger, especially if he is a Trinitarian?
Answer: “It is well-known that the testimony that there is no Deity worthy of worship except Allah and Muhammad is the Messenger of Allah is required. If a person bears witness that Muhammad is the Messenger of Allah then whatever comes after that follows it. However, mentioning what we are discussing now [of the aforementioned phrase] and requesting [that a Christian say it] is desirable, but not necessary (i.e. a must).” [Sharh Sunnan at-Tirmidhi (no. 281)]
Thus, if a Christian professes that ‘Isa (Jesus) is Allah’s Slave and His Messenger alongside the Shahaadah then this is good. However, if they pronounce the Shahaadah as it is while believing that ‘Isa is Allah’s Slave and Messenger, then that is sufficient.
And Allah Knows Best
Faisal bin Abdul Qaadir bin Hassan