Was there a Companion who feared or was unable to fight, and what was the reason, and is there a narration that indicates this?

Hassan ibn Thabit (may Allah be pleased with him) strove with his self and his tongue. The evidence of his striving is what Al-Dhahabi said in his biography of him: From Sa'id ibn Jubayr, he said: It was said to Ibn Abbas: "Hassan the accursed has come!" Ibn Abbas said: "He is not accursed; he strove alongside the Messenger of Allah (peace and blessings of Allah be upon him) with his self and his tongue." It is said that the reason for his not striving (with his body in battle) was that he was afflicted with an ailment that made him cowardly.