Umar Ibnul Khattaab [radiyallaahu-anhu] said:

The best of deeds is the fulfilment of what Allaah has made obligatory, refraining from what Allaah has forbidden out of fear of Him and having a truthful intention in [hoping] for what Allaah has with Him [of reward in the hereafter].

[Jaami-ul Uloom Wal-Hikam:page:379]