Is the Udhiyah valid and sufficient for everyone if three people share a cow, with each intending to sacrifice one-third, and then a fourth person joins one of them, sharing their third equally between them, or is it not sufficient for everyone, or is it not sufficient only for the fourth person?

According to the majority of scholars, a cow suffices as an udhiyah (sacrificial animal) for seven people, unlike the view of the Malikis. The majority relies on the hadith narrated by Jabir in Sahih Muslim: "We sacrificed with the Messenger of Allah, peace and blessings be upon him, in the year of Al-Hudaybiyah, a camel for seven and a cow for seven." This applies to the hady (sacrifice offered during Hajj), and the udhiyah is analogous to it.