Narrated Abu Hurairah (radiyAllahu anhu): Allah's Messenger (sallAllahu 'alayhi wa sallam) said, "Allah the Exalted has said: 'I will declare war against him who shows hostility to a pious worshipper of Mine. And the most beloved thing with which My slave comes nearer to Me, is what I have enjoined upon him; and My slave keeps on coming closer to Me through performing Nawafil (voluntary prayers or doing extra deeds besides what is obligatory) till I love him, (so much so that) I become his hearing with which he hears, and his sight with which he sees, and his hand with which he strikes, and his leg with which he walks; and if he asks Me something, I will surely give him, and if he seeks My Protection (refuge), I will surely protect him.'"

(Sahih Bukhari)