As salaam Alaykum. I was reading Surah Yusuf and I wanted to know if the bad treatment of Yusuf’s brothers towards their father Yaqub (peace be upon them both) constituted disbelief since he was a prophet.

All perfect praise be to Allah, The Lord of the Worlds. I testify that none is worthy of worship except Allah and that Muhammad is His slave and messenger.

No scholar has ever said that the brothers of Yoosuf had disbelieved because of what they had done. However, they had committed a grave major sin, which they did as a result of giving in to their desires, as they wished to be the ones with the closest rank to their father Ya'qoob (Jacob ).

Al-Qurtubi said in his Tafseer (interpretation of the Quran) about the verse that says (what means): {Indeed, our father is in clear misguidance.}: “They were not referring to the misguidance in religion, because if this is what they had intended, they would have become disbelievers. Rather, they wanted to say that their father did not run the affairs appropriately as he favored two of his sons over ten others while they were all his sons. Another intepretation says that they meant that he (Ya'qoob) had committed a clear mistake by favoring Yoosuf and his brother over them.” [End of quote]

This is explicit and clear that they did not become disbelievers by their statement.

Allah knows best.