Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 1 year ago
Bismihi ta'ala
Ghusl janabah will not become wajib unless there is ejaculation, or penetration.
The amount of penetration is the glans penis, which is the tip or top portion of the penis (called ḥashafah).
If there is penetration, to that extent or more, ghusl janabah becomes wajib upon both husband and wife.
And Allah knows best.