When anyone wants to attain ... purity he should attend first to his clothes. Merely reading and learning about these visible things does not cause them to be realized: It is necessary to bestir oneself as much as possible and show oneself assiduous in renewing ablutions. ... At the end of the night, toward dawn, let him take a bath. Let him consider this a good work. Almighty God will adorn him with a special kind of purity and will remove all external and internal pollution. 
It is related that Khwaja Bayazid said: "Whenever any thought of the world enters my heart, I cleanse myself, and whenever any thought about the world to come enters my heart, I take a bath." The reason is that the world is polluted and any thought about it is polluting. Hence cleansing or purification becomes necessary. In the life to come there is carnal desire, and one must obtain relief from that ceremonial pollution. While it is necessary to be cleansed from what pollutes, a bath is needed once ceremonial pollution has occurred.
The sheikhs have insisted on the necessity of both external and internal purification and have laid great stress on it. The starting point for those desiring to follow the Way is that their hearts become mirrorlike, so clean and shining that one can see reflected in them an image of the world of creatures and of the divine order. Thus they progress from the ranks of commoners to the rank of the elect. 
[The traveller on the way] should purify himself, as if he were performing the ablutions from major ritual impurity (al-janaaba), for man, so long as he remains pre-occupied with the world and those matters which distract from God Most High, will be ruled over by impurities (al-junub). But if he desires to stand before God Most High, he must of neccessity cleanse himself of ritual impurity with water as does the one about to pray. He should recite before beginning the ritual ablution,
O God, Cleanse me of every impurity, every error (hadath), every malady ('illa), every sickness (marad), every sin (dhanb), every act of disobedience (ma'siya), every negligence (ghafla), every transgression (zulma), every veil (hijaab), every estrangement (qati'a); indeed everything of which Thou cleansed Thy Prophet, Muhammad, May God bless and grant peace to his family, outwardly and inwardly, O Lord of the Worlds.
1. Maneri, Sharafuddin. The Hundred Letters. Pg 111
2. Pg 115-116
3. Pg 118
4. Enigmatic Saint: Ahmad ibn Idris and the Idrisi Tradition. Pg 204-205.