Response: I do not know of any basis for this name from the Sunnah, that the mount which is in‘Arafah at which the Prophet (sal-Allaahu `alayhe wa sallam) stood is called Jabal ar-Rahmah. If there is no basis for it in the Sunnah then it is not befitting to apply this (name) to it. Those who have applied this name, then they have possibly observed that this is a great (standing) place which is recognised as a place of Allaah’s Forgiveness and Mercy for those standing upon it in‘Arafah. Therefore, they named it such. So that which is better is to not call it by this name, rather, call it Jabal ‘Arafah, or the mount at which the Prophet (sal-Allaahu `alayhe wa sallam) stood or that which is similar to this.
Shaykh Ibn ‘Uthaymeen
Daleel al-Akhtaa.a yaqa’a feehaa al-Haaj wal-Mu’tamir wat-tahdtheer minhaa – Page 69.fatwaonline.com