The scholars are unanimously agreed that ghusl is required in the event of intercourse.
Al-Mawsoo’ah al-Fiqhiyyah, 3/198
If a man has intercourse with his wife, they must both do ghusl even if there is no ejaculation. This was narrated clearly from the Prophet (peace and blessings of Allaah be upon him) in the report narrated by Abu Hurayrah (may Allaah be pleased with him), according to which the Prophet of Allaah (peace and blessings of Allaah be upon him) said: “When a man sits between the four parts (arms and legs of his wife) and has intercourse with her, then ghusl is obligatory.” Narrated by al-Bukhaari, 291. Muslim added (525): “Even if he does not ejaculate.”
Al-Nawawi said in Sharh Muslim:
What this hadeeth means is that the obligation of ghusl does not depend on the emission of semen, rather when the tip of the penis disappears into the vagina, then ghusl becomes obligatory for both the man and the woman. There is no dispute concerning this matter today, although there was a difference of opinion among the Sahaabah and those who came after them. Then there arose consensus on what we have mentioned. End quote.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
It is clear that ghusl is required in this case, even if he does not ejaculate. This is something that is not known to many people, so you may find that this has happened to a couple, but they do not do ghusl, especially if they are young and have not learned much. This is based on their idea that ghusl is only required when ejaculation takes place, but this is wrong. End quote.
Al-Sharh al-Mumti’, 1/223
It says in Fataawa al-Lajnah al-Daa’imah (5/314):
Among the things that make ghusl obligatory for a Muslim are: the emission of semen whilst sleeping; the disappearing of the tip of the penis into the vagina even if no ejaculation takes place; the emission of semen with pleasure when one is awake, even if no intercourse takes place; and menses and nifaas (postpartum bleeding) in the case of a woman, in which case she must do ghusl when the bleeding stops.”