Volume 1, Book 4, Number 243:

http://www.holyebooks.org/islam/hadith_of_bukhari/004.sbt.html

What is Intoxication

A state in which a person's normal capacity to act or reason is inhibited by alcohol or drugs. 

Generally, an intoxicated person is incapable of acting as an ordinary prudent and cautious person would act under similar conditions. In recognition of this factor, the law may allow intoxication to be used as a defense to certain crimes. In many jurisdictions, intoxication is a defense to specific-intent crimes. The underlying rationale is that the intoxicated individual cannot possess the requisite mental state necessary to establish the offense