Assalaamualaikum wa Rahmatullahi wa Barakaatuh, I have read on some websites that the true Testimony of Faith (Ash-Shahadah) is 'Laa ilaaha illallah', and on other websites that 'Ashhadu allaa ilaaha illallahu wa ashhadu anna Mugammadan abduhu wa rasooluh' is the true Testimony. Please provide me with Quran and hadith quotes that states what the true Testimony is. And also, please provide me with hadith that states what one who reverts to Islam should recite. Jazakallahu Khayran. Thank you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The Testimony of Faith by which a non-Muslim enters Islam is to say: Ashhadu an laa ilaaha illa Allaah wa anna Muhammadan Rasool Allaah; which means that none has the right to be worshipped but Allaah and that Muhammad is the Messenger of Allaah. The first Testimony means affirming and having a firm belief that it is Allaah alone Who is worthy of worship, and the second Testimony means affirming and having a firm belief that Muhammad is truly a Messenger sent from Allaah. Indeed, the Prophet, sallallaahu ‘alayhi wa sallam, used to call the non-Muslims to these Two Testimonies of Faith as in the Hadeeth by Ibn 'Abbaas when the Prophet, sallallaahu ‘alayhi wa sallam, sent Mu‘aath to Yemen and he told him to invite them to the Testimony (that none has the right to be worshipped but Allaah and that I am the Messenger of Allaah). [Al-Bukhari and Muslim]

Also, non-Muslims used to embrace Islam with these two Testimonies at the time of the Prophet, sallallaahu ‘alayhi wa sallam, and there are many narratives about this:

1- The story of Thumaamah embracing Islam reported by Al-Bukhaari, which reads: “.... then he entered the mosque and said: ‘Ashhadu an laa ilaaha illa Allaah wa anna Muhammadan Rasool Allaah.’”

2- The story of ‘Abdullaah ibn Salaam when embracing Islam; he said: “Ashhadu an laa ilaaha illa Allaah wa annak Rasool Allaah (and that you are the Messenger of Allaah.)” [Al-Bukhari]

3- The story of the Jewish boy whom the Prophet, sallallaahu ‘alayhi wa sallam, visited when he was on his deathbed, and the boy said: “Ashhadu an laa ilaaha illa Allaah wa ashhadu annaka Rasool Allaah (and that you are the Messenge of Allaah),” so the Prophet, sallallaahu ‘alayhi wa sallam, came out and said: “Praise to Allaah Who saved him by me from the Fire.” [Ahmad] In the narration reported by Al-Haakim, it reads: the Prophet, sallallaahu ‘alayhi wa sallam, said to the boy: “Say, Ashhadu an Laa ilaaha illa Allaah wa annak Rasool Allaah.” So the Jewish boy looked at his father who told him: “Say what Muhammad is saying to you.”

Imaam An-Nawawi said in his commentary on Muslim's Saheeh: “The adepts of the Sunnah among the scholars of Hadeeth, Fiqh and 'Ilm al-Kalaam (Islamic theology) unanimously agreed that the believer who is deemed to be from the people of the Qiblah and who does not abide eternally in Hellfire is the one who believes in his heart in the religion of Islam, with a strong belief that is free from doubts, and who uttered the Two Testimonies of Faith. If one only utters one Testimony, he is not among the people of the Qiblah (i.e. he is not a Muslim) at all unless he is unable to utter it due to a defect in his tongue or. . . because of undergoing the pain of death due to his soul leaving his body or due to other reasons, in which case, he is considered a Muslim. . . ; however, if he only utters Laa ilaaha illa Allaah, and he does not utter 'Muhammadun Rasool Allaah, i.e. Muhammad is the Messenger of Allaah', then the well-known view in our School and the view of the scholars is that he is not a Muslim. But there are some scholars from our school who said he is considered a Muslim but he will be required to utter the other testimony. If he refuses, he is considered an apostate.” [End of quote]

For clarification that the Two Testimonies of Faith are linked together, and that there is no salvation except by worshipping Allaah alone and following the guidance of the Prophet, sallallaahu ‘alayhi wa sallam, please refer to Fatwa 117537.

Allaah Knows best.