It is the best of righteous deeds
On the authority of Abu Dharr who said: ‘I said:
O Messenger of Allaah advise me.’
The Messenger -sallAllaahu alayhi wa sallam – said: ‘If you do a bad deed then follow it up with a good one and it wipes it out.’
Abu Dharr continued: I said: ‘O Messenger of Allaah is ‘La ilaha illa Allaah’ from the good deeds?’
He answered: ‘It is the best of righteous deeds.’
Narrated by Ahmad and al-Albani graded it Hasan in ‘Saheehah’ (1373).