Is self-harm with a knife due to depression and sadness, followed by regret, considered among the forbidden acts of impatience during affliction? And does patience after this act necessitate the reward mentioned in the Hadith: "Indeed, patience is at the first strike of a calamity"?

When afflicted, a believer must turn to their faith, surrender to Allah's decrees, and patiently endure His judgment. Self-harm is forbidden, and you have committed a grave error by injuring yourself. However, since you have repented and regretted your action, Allah Almighty will accept your repentance, for "the one who repents from a sin is like one who has no sin." You might have missed the reward for patience at the first shock, but after your repentance, patience, and seeking reward from Allah, you are on the right path, and you will not miss the reward of the patient, Allah willing.