All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.
Cursing Allaah The Exalted is a major sin that turns a person into a disbeliever who should then be asked to repent, and if he refuses, he should be killed.
However, as long as you sincerely repented to Allaah The Almighty and are honestly determined not to commit this sin again, then Allaah The Almighty will forgive you and be pleased with your repentance. Allaah The Almighty Says (what means):
· {Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allaah. Indeed, Allaah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful."} [Quran 39:53]
· {And turn to Allaah in repentance, all of you, O believers, that you might succeed.} [Quran 24:31]
This ruling applies only if you committed this sin after puberty. If you committed it before that you have not sinned, if Allaah wills. It was narrated on the authority of ‘Aa'ishah, the mother of believers that the Prophet, sallallaahu ‘alayhi wa sallam, stated that the recording pen is lifted for three types of people: the one who is sleeping until he wakes up, the child until he reaches puberty, and the insane until he becomes sane. [Ahmad, Abu Daawood, An-Nasaa'i, At-Tirmithi and Ibn Maajah in their books of Sunan] [Al-Haakim: Saheeh (Authentic)]
Allaah Knows best.