[The Meaning of: “Do not curse Time, for verily Allah is Time”]

Answer: The people in those times used to attribute the calamities of death, afflictions, poverty, old age, weakness, greyness of hair, decrepitude, and the like, to “Time (al-dahr)”. So if something of that befell one of them, he would curse Time, because in his view it was Time that had done that. For that reason – and Allah knows best – the Prophet (May Allah bless him and his family and grant them peace) said to them: “Do not curse Time, for Time is Allah,” meaning: the One who has done to you those trials and calamities is Allah. So if you curse Time, you have cursed Allah, because He is the One who truly does what you think is from “Time”.
A similar example is that you might say to someone whose leg is hurting him, thinking that its pain came from a thorn: “The thorn is the snake,” intending that the pain that occurred in his leg was not from a thorn, but rather from a snake; you do not intend that the thorn’s name is “snake”. Likewise is what has come in the hadith.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3