In Jainism, "rātri-vihāra" refers to the practice of moving or traveling at night, and it is generally prohibited for Jain monks (munis) and nuns. Jain rules of conduct (ācāra) strictly instruct monks and nuns to avoid traveling after sunset and before sunrise. This is primarily based on the principle of ahimsa (non-violence).

Reasons for Avoiding Ratri Vihar:

1. Non-violence (Ahimsa): At night, visibility is low and there is a higher chance of unintentionally harming small insects and living beings that are more active or less visible in the dark. Avoiding travel at night minimizes the risk of violence.

1. Safety and Discipline: Traveling at night can be dangerous and may compromise the safety and discipline of monks, who are expected to live a life of careful awareness and restraint.

1. Tradition and Scriptural Instruction: Jain scriptures like the Ācāranga Sūtra and other conduct manuals (Cheda-sutras) clearly prohibit night travel for ascetics.

Exceptions: There are rare and exceptional circumstances (such as during emergencies or to avoid danger) where rātri-vihāra may be permitted, but these are strictly regulated and allowed only under specific conditions as per the guidance of Jain acharyas (spiritual leaders).

In summary: Most Jain munis do not practice ratri vihar; instead, they avoid it as an essential part of their code of conduct, rooted in the principle of non-violence and scriptural discipline.