苦行僧（Sadu）是印度盛行的修练方式，常有苦行僧蓬头垢面、衣衫褴褛，带着象征湿婆裨的三叉杖，边走边吟诵古经文。苦行僧必须忍受常人认为是痛苦的事，如长期断食甚至断水、躺在布满钉子的床上、行走在火热的木炭上、喝尿吃屎、忍酷热严寒等事情，来锻炼忍耐力和离欲。

一般婆罗门尊崇苦行僧，但是大多数的婆罗门都不是苦行僧。耆那教有两派别，天衣派主张苦行，白衣派不主张苦行．释迦牟尼成佛前曾修苦行，「昼便入林中。夜便露坐……至冢间。取彼死人之衣。而覆形体……日食一麻一米。形体劣弱。骸骨相连。顶上生疮。皮肉自堕。犹如败坏瓠卢……」。后来发现修苦行并不能达到究竟，于是转以其他方法修行成佛．释迦牟尼佛曾在优罗毗罗村收留五名苦行僧，此为佛经上记载的「初转法轮」。

In Hinduism, a sādhu (Sanskrit sādhu, "good; good man, holy man") is a religious ascetic or holy person. Although the vast majority of sādhus are yogīs, not all yogīs are sādhus. The sādhu is solely dedicated to achieving mokṣa (liberation), the fourth and final aśrama (stage of life), through meditation and contemplation of Brahman. Sādhus often wear saffron-coloured clothing, symbolising their sannyāsa (renunciation). This way of life is open to women; the female form of the word is sādhvī. In 2014, an all-female akhada (group of sadhus) was formed; it is believed to be the first such group in India.