What is the ruling regarding someone who saw in their dream that they were cursing the Lord?

A sleeping person is not held accountable for what they see or say in their dreams, due to the hadith (definition): "The pen has been lifted from three: from the insane person... and from the sleeper until he awakens..." What the questioner saw is a dream from Satan to grieve the believer, for the Prophet, peace and blessings be upon him, said: "Visions are three: a righteous vision is good tidings from Allah, a vision of grief is from Satan, and a vision of what a person talks to himself about. So if any of you sees something he dislikes, let him get up and pray and not tell people about it." Therefore, what you saw in the dream does not harm you.