What is the "insanity" meant in the hadith: "The pen has been lifted from three... and from the insane until he recovers"? Does this include mentally ill individuals such as those suffering from depression, schizophrenia, or obsessive-compulsive disorder, especially since these illnesses are accompanied by a disturbance in brain chemistry?

The pen is lifted from the insane until they recover, due to their loss of intellect, which is the basis of accountability. A patient suffering from depression or obsessive-compulsive disorder, if their illness reaches the point of mental incapacitation, is among those from whom the pen is lifted during the period of their mental absence. However, if their intellect is not absent, but they are unable to perform some or all of their religious obligations, the fundamental obligation of accountability does not fall away from them. Rather, they are permitted to perform these obligations to the best of their ability. Some acts of worship may even be waived entirely if they are completely unable to perform them, and they may resort to a substitute if one exists, based on the Almighty's saying: "Allah does not burden a soul beyond its capacity," and the Prophet's (peace be upon him) saying: "When I command you to do something, do of it as much as you are able."