Adding his name to the First Pillar of Islam ( Shahada )

(i) It is narrated on the authority of 'Abdullah son of 'Umar that the Messenger of Allah (may peace be upon him) said: (The superstructure of) al-Islam is raised on five (pillars), testifying (the fact) that there is no god but Allah, that Muhammad is His bondsman and messenger, and the establishment of prayer, payment of Zakat, Pilgrimage to the House (Ka'ba) and the fast of Ramadan.
Sahih muslim Book 001, Number 0020

Hadith V/S Hadith

(i) Narrated Anas: The Prophet said, “Whoever said “None has the right to be worshipped but Allah (LA ILAHA ILL – ALLAH) and has in his heart good (faith) equal to the weight of a barley grain will be taken out of Hell. And whoever said: “None has the right to be worshipped but Allah and has in his heart good (faith) equal to the weight of a wheat grain will be taken out of Hell. And whoever said, “None has the right to be worshipped but Allah and has in his heart good (faith) equal to the weight of an atom will be taken out of Hell.”
Sahi Bukhari Volume 1, Book 2, Number 42

(iv) Narrated Zainab bint Jahsh:

The Prophet got up from his sleep with a flushed red face and said, "None has the right to be worshipped but Allah (LA ILAHA ILL – ALLAH). Woe to the Arabs, from the Great evil that is nearly approaching them. Today a gap has been made in the wall of Gog and Magog like this." (Sufyan illustrated by this forming the number 90 or 100 with his fingers.) It was asked, "Shall we be destroyed though there are righteous people among us?" The Prophet said, "Yes, if evil increased."
Sahih Bukhari, Volume 9, Book 88, Number 181