Abu Hurairah, radiyallahu 'anhu, reported that the Messenger of Allah, sallallahu 'alayhi wasallam, said:
"Allah the Almighty has said: 'Whosoever acts with enmity towards a closer servant of Mine (wali), I will indeed declare war against him. Nothing endears My servant to Me than doing of what I have made obligatory upon him to do. And My servant continues to draw nearer to Me with supererogatory (nawafil) prayers so that I shall love him. When I love him, I shall be his hearing with which he shall hear, his sight with which he shall see, his hands with which he shall hold, and his feet with which he shall walk. And if he asks (something) of Me, I shall surely give it to him, and if he takes refuge in Me, I shall certainly grant him it.'"
It is mentioned in the 40 Hadith of Rasoolullah (sallallahu 'alaihi wasallam) by Imam Nawawi (rahmatullahi 'alaihi)
On the authority of Abu Najih Al-Erbadh bin Sariah, who said :
The messenger of Allah gave us a sermon by which our hearts were filled with fear and tears came to our eyes. We said: "O Messenger of Allah, it is as though this is a farewell sermon, so councel us." He said: "I councel you to fear Allah and to give absolute obedience even if a slave becomes your leader. Verily he among you who lives [long] will see great controversy, so you must keep to my sunnah and to the sunnah of the rightly-guided Khalifahs - cling to them stubbornly. Beware of newly invented matters, for every invented matter is an innovation and every innovation is a going astray, and every going astray is in Hell-fire."
related by Abu Dawud and Al-Tirmithi, who said that it was a fine and true Hadith.