These disciples of God who are termed as Sufis have in seclusion (chillah) perfected withdrawal of senses of perception from seeking sense gratification from the external environment.
Prophet Muhammad used to go to the cave of Hira and pass days and nights in Khilvat. When he was forty years old, he received the first Divine relevation in the cave of Hira. This tradition of khilvat is firmly held by the Sufis who also go into retreat once every year.
The Sufis go into Khilvat for 40 days in a year. Here moral injunction and fixed observances are adhered to and the disciples try for greater perfection in improving the concentration on the Divine (Fikr) with increased practice of Zikr (rememberance of the Divine). In khilvat the disciple also is able to isolate the voice of the soul which is different from the ordinary thought of the mind or the voice of the ego or the voice of the intelligence.
We must remember here that the disciples who go in Khilvat have already the blessings of Murshid (spiritual mentor) for it is not possible without the guidance from the murshid to be able to isolate the intution from the Jungle of other voices in the mind which originate due to imagination of hallucination or from mental fatigue. In khilvat the negative traits retarding the progress of the murid (disciple) are weeded out for it is only in isolation that perfect concentration with perfect contemplation combine to enhance Zikr (remembrance of the Divine).