It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever insults a friend (wali) of Mine has declared war on Me. O son of Adam, you will not attain what is with Me except by fulfilling what I have made obligatory upon you. My servant continues to seek My love through voluntary deeds until I love him; then I become his heart with which he understands, his tongue with which he speaks, and his sight with which he sees. Then when he calls upon Me, I answer him; when he asks of Me, I give him; and when he seeks My help, I help him. And the most beloved worship of My servant to Me is sincere goodwill."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7849