signs, symptoms and cures of the spiritual diseases of the heart
The next disease is when one's heart is engaged in matters that are of no concern to him. In essence, if an action is forbidden, reflecting on that action is also forbidden.
For example, reflecting on things that are prohibited, such as lustful fantasizing about the beauty of a person one is not married to.
Thinking about the weaknesses or faults of others is forbidden, whether they are present or not.
It is also prohibited, according to scholars, to reflect on the nature of God's essence. This does not mean that one should not reflect on His attributes revealed in the Qur'an. Rather, trying to conceive of the very essence of God is beyond our capability, and so our conclusions will always be wrong. Being wrong about something like this is not inconsequential. Many religious communities before Islam as well as after indulged in this activity and have come up with terribly erroneous theologies regarding God. For this reason, we are told to stay away from that kind of internal or external dialogue [...]
Spending time thinking or talking about other people's faults is foolish. Time is short and is better invested in recognizing one's own shortcomings and then working consistently to eradicate them.
Reflect on what God has revealed about Himself and His awesome majesty, knowledge, and power. That kind of reflection deepens one's love of Him and one's desire to follow His commandments and thus prepare for the Hereafter, a momentous time when the veils will be removed from our eyes and when our understanding of God will reach beyond what is possible in this world.
"There is a tree in Paradise reserved for one whose own faults preoccupied him from considering the faults of others" (The Prophet ﷺ)