Purity: Janabah via Sexual Intercourse
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 348:
If a person has sexual intercourse with a woman and penetration occurs up to or more than the circumcised part of the penis – irrespective of whether the penetration was in the vagina or the anus, and whether the man had reached the age of legal responsibility (bulūgh) or not – then, even if semen is not ejaculated, both the man and the woman become junub.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)