Exodus 21:19

על משענתו (lit., with that on which he relies) — i. e. his former healthy state and vigour (Mekhilta; cf. Onkelos). ונקה המכה [WHEN HE RISES AGAIN…] HE THAT SMOTE HIM SHALL BE FREED — But could it enter your mind that this person who has not killed anyone at all should be subject to the death penalty? Why, then, is it necessary to state this? But it is intended to teach you that he is kept in prison until we discover whether the other is completely healed or not, and what the verse implies is this: when this man rises again (אם יקום) and walks in the street in his former vigour, then he who smote him shall be freed from prison, but so long as the other has not risen from the sick-bed etc. the man who smote him is not freed (Ketubot 33b; Sanhedrin 78b). רק שבתו ONLY [HE SHALL PAY FOR] THE LOSS OF HIS TIME — i. e. for the interruption of his labour due to this illness. If, for instance, he cut off his hand or his foot, we regard the interruption of labour caused by this illness as though his occupation were that of a watchman in a cucumber field (which work can be done even by a man lacking a hand or a foot), for even after he has recovered from the illness he will not be able to do work which requires hands or feet, and indeed the value of his hand or his foot that was cut off the other has already paid to him as “damages” (נזק), as it is said, (v. 24) “hand for hand, foot for foot”. (Having compensated him already for loss of capacity as a wage-earner whole in body, it would not be right if this man has again to pay him for loss of time as though he were of full-earning capacity) (Bava Kamma 85b). ורפא ירפא — Translate it as the Targum does: he shall pay the physician’s fee.

אִם־יָק֞וּם וְהִתְהַלֵּ֥ךְ בַּח֛וּץ עַל־מִשְׁעַנְתּ֖וֹ וְנִקָּ֣ה הַמַּכֶּ֑ה רַ֥ק שִׁבְתּ֛וֹ יִתֵּ֖ן וְרַפֹּ֥א יְרַפֵּֽא׃ {ס}        

if he rise again, and walk abroad upon his staff, then shall he that struck him be acquitted: only he shall pay for the loss of his time, and shall cause him to be thoroughly healed.