Which is more appropriate when catching a thief: releasing him as an act of clemency, or handing him over to the competent authorities to implement the ruling of Sharia?

If the one who apprehends the thief is not the ruler or his deputy, it is better to advise him, cover his deed, and not refer him to the ruler. For once the matter is referred, forgiveness is no longer permissible, and the ḥadd punishment must be carried out. Safwan ibn Umayya narrated that the Messenger of Allah ﷺ ordered his hand to be cut off for stealing his cloak. Safwan said: "I did not intend this, O Messenger of Allah; it is a charity from me to him." The Messenger of Allah ﷺ said: "Why didn't you do so before bringing him to me?" Covering a sin is recommended as long as the matter has not reached the Imam. An exception to this is made for those known for evil and harm; in their case, it is better to refer them to the ruler to curb their evil.