Chilla (Persian: چله, Arabic: أربعين, both literally meaning "forty"), also referred to as Chilla-nashini, is a spiritual discipline observed in Sufism, prevalent in Indian and Persian traditions. In this ritual, a mendicant or ascetic endeavors to maintain a seated position within a circle, engaging in meditation techniques without consuming food for a continuous period of 40 days and nights, mirroring the observance of Arba'een.

In the practice phase, individuals aspiring to become professional musicians undertake a vow known as Cillā, lasting for forty days. This commitment involves sacrificing hours of sleep and eating to dedicate ample time daily for practicing the skills acquired over years of learning.

The Cillā is frequently sustained, sometimes without interruption, for an extended period—lasting five, ten, or even twelve years—before the mentor grants approval for a public performance.