IPC Section 87

Nothing which is not intended to cause death, or grievous hurt, and which is not known by the doer to be likely to cause death or grievous hurt, is an offence by reason of any harm which it may cause, or be intended by the doer to cause, to any person, above eighteen years of age, who has given consent, whether express or implied, to suffer that harm;
Or by reason of any harm which it may be known by the doer to be likely to cause to any such person who has consented to take the risk of that harm.