The Sahabi who killed his own father was Abu Ubayda ibn al-Jarrah (RA). This occurred during the Battle of Badr, where Abu Ubayda's father was fighting against the Muslims. Faced with the choice of defending his faith or protecting his father, Abu Ubayda chose the former and ultimately had to kill his father in battle.
This event exemplifies the immense loyalty and commitment that the Sahabah displayed to their faith and the Prophet Muhammad (PBUH). While this was a deeply painful and difficult choice, Abu Ubayda's actions demonstrated the true meaning of sacrifice and dedication in the face of conflict.