Was Zain al-Abidin a coward for leaving his father to be killed in Karbala without helping him?

Zayn al-Abidin Ali ibn al-Husayn was a man of virtue, piety, and devotion. Imam al-Zuhri described him as the best Qurayshi he had ever seen. As for accusing him of cowardice and abandoning the fight with his father, this is a pure fabrication. He was ill on the day of Karbala and did not fight, and no one confronted him.