The way to achieve Ikhlaas and protect from losing reward during deeds

Shaykh ibnu Uthaymeen said:
The way that saves a person from this is to seek refuge in Allah from the shaytaan the cursed and to seek his aid in carrying out his obedience. Also a person should not pay attention to the whisperings which the shaytaan throws at his heart, for indeed the shaytaan does this to ruin and corrupt his worship and intention, therefore he should discard them and don’t pay attention to them. 

Perhaps a person may find difficulty in rectifying their intention but if he continues and is patient, then the final destination is for those who have Taqwa. Some of the Salaf use to say: “I have not strived with myself with anything more than Ikhlaas (sincerity)”. But he succeeded. 

So if a person continues with the action he is performing, seeks refuge in Allah from the shaytaan, seeks Allah’s aid in his obedience and is patient and forbearing, then indeed Allah will give him safety and success.
Fataawaa Noor Alaa Ad-Darb (12/11)