Purity: Causes of Janabah (Ritual Impurity)
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 344:
A person becomes junub[1] in two ways:
1. Sexual intercourse;
2. Ejaculation of semen, whether he is asleep or awake, and whether it is a little or a lot, with or without lust, voluntarily or involuntarily.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)
1
Junub is the term used to refer to a person who is in the state of janābah.