Sahih Muslim Book 035, Hadith Number 6474.

Chapter : Exhortation for the remembrance of Allah, the Exalted.

Abu Huraira reported that Allah's Messenger (may peace be upon him) was travelling along the path leading to Mecca that he happened to pass by a mountain called Jumdan. He said: Proceed on, it is Jumdan, Mufarradun have gone ahead. They (the Companions of the Holy Prophet) said: Allah's Messenger, who are Mufarradun? He said: They are those males and females who remember Allah much.