Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
One of the mercies of the Shari`ah is that it takes into account human weaknesses. As Aishah, Allah be pleased with her, informs us that the laws were revealed gradually. In earlier times, rules were more or less relaxed; however, they became stricter later.
When seen in this way, we can very well understand why some of the companions initially thought that bathing was only obligatory in case of intercourse followed by ejaculation. They had no idea it had been abrogated. As we read the Prophet, peace be upon him, ordered them to perform ghusl, following vaginal penetration, whether it resulted in ejaculation or not.
That is why we learn from other reports that the companions who held the former view accepted the correction when it was pointed out to them.
Therefore, we ought to follow the latter view: Ghusl is obligatory in case of vaginal penetration, whether it was accompanied by seminal emission or not. Therefore, we must abide by the latter rule.
Almighty Allah knows best.
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