The Prophet (sal Allahu alaihi wa sallam) said: “It is obligatory upon every adult to take a bath on Friday and to brush their teeth and use perfume if available.” [Bukhari]
Cleanliness has been equated in Islam with half of Eeman (faith). To ensure this, we have to clean our bodies, clothes and prayer surroundings five times a day, i.e. before each prayer. The prayer then purifies us spiritually.
This Hadith sets the minimum thorough bathing limit at once a week. Every physically adult Muslim must labour to clean their hair, body, teeth and use (oil-based) perfume, if they have it, at least every Friday.