Virtue of 'Laa ilaaha illalLaah'
Messenger of Allaah (peace and blessings of Allah be upon him) said, "Allaah has forbidden the Fire for the one who said 'Laa ilaaha illalLaah' seeking by that Allaah's Face." (Al-Bukhaaree and Muslim)
Al-Hasan Al-Basree said, "Some people say: whoever says 'Laa ilaaha illalLaah' shall enter Paradise.' [But the truth is that] whoever says 'Laa ilaaha illalLaah' and fulfils its rights and obligations shall enter Paradise."
Someone asked Wahb ibn Munabbih as to whether saying 'Laa ilaaha illalLaah' is the key to Paradise. He answered in the affirmative but added, "There is no key that has no prongs. If you bring a key that has prongs it will open the door for you and if you do not, it will not open the door for you."
The Prophet said, "The testimony that there is no deity worthy of being worshipped except Allaah and that I am the Messenger of Allaah: No slave meets Allaah with this [belief], having no doubt in them except that he enters Paradise." (Muslim)
The Prophet said, "No one testifies that there is no deity worthy of worship except Allaah and that Muhammad is the slave of Allaah and His Messenger, truthfully from his heart except that Allaah forbids Hell-Fire for him."