Reward of reciting 'La illaaha illallah' loudly

1. Imam Jafar as-Sadiq (a.s) says, "The Holy Prophet (saw) said, 'A person who recites 'La illaaha illallah' is free. He crushes his sins with his feet and destroys them in the same way as dry leaves fall off from a tree."
2. The Messenger of Allah (saw) says, "Allah likes the statement of 'La illaaha illallah' much more than any other statement in this world. The sins of the person who recites 'La illaaha illallah' are wiped out in the same way as dry leaves fall off a tree."
3. The Messenger of Allah (saw) says, "One who does not recite 'La illaaha illallah' is proud and arrogant."

Ref: Sawaabul Aamaal and Iqaabul Aamaal

Reward for reciting 'La illaaha illallah' with Sincerity

Imam Jafar as-Sadiq (a.s) says, "A person who recites, 'La illaaha illallah' with pure intention will enter Paradise and reciting 'La illaaha illallah' with pure intention implies that he keeps away from that, which Allah has prohibited for him."

Reward of reciting 'La ilaaha illallah' a hundred times

1. Imam Jafar as-Sadiq (a.s) says, "The deed of one who recites 'La illaaha illallah' a hundred times is better than all except one who recites it more than a hundred times."
2. Imam Jafar as-Sadiq (a.s) says, "Allah builds a house in paradise for one who recites 'La illaaha illallah' a hundred times before going to bed. And the sins of one who recites Astagfirullah a hundred times before going to bed are destroyed in the same way as dry leaves fall off from a tree.

Ref: Sawaabul Aamaal and Iqaabul Aamaal