This questioner - may Allah guide him - does not realise that he has already disobeyed Allah, may He be exalted, by saying this even if he has not committed the sins that he stated clearly he would commit.
It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: Allaah, may He be glorified and exalted, will forgive my ummah for whatever crosses their minds so long as they do not act upon it or speak of it.
Narrated by al-Bukhaari, 4968; Muslim, 127.
Shaykh al-Islam Ibn Taymiyah said:
(The Prophet (blessings and peace of Allah be upon him)) has told us that Allah forgives whatever crosses a person's mind so long as he does not speak of it. So a distinction is made between thoughts that cross the mind and words that are spoken. And he told us that he will not be blamed for a passing thought unless he speaks of it. What is meant is unless his tongue utters it, according to scholarly consensus.
End quote from Majmoo al-Fataawa, 7/133
It was narrated from Abu Kabshah al-Anmaari that he heard the Messenger of Allah (blessings and peace of Allah be upon him) say: People of this world are four types: a man to whom Allaah gives wealth and knowledge, so he fears his Lord concerning it, upholds ties of kinship with it and realizes that something is due to Allah for that. This man will attain the highest status. (The second is) a man to whom Allaah gives knowledge but He does not give him wealth, but he is sincere in intention and says: If I had wealth, I would have done what (the first man) did. He will be judged according to his intention and their reward will be the same. (The third one is) a man to whom Allah gives wealth but does not give knowledge, so he squanders his wealth without knowledge and does not fear Allah concerning it or uphold ties of kinship with it, and he does not realize that something is due to Allah for that. His will be the lowest status. (Then there is) a man to whom Allah gave neither wealth nor knowledge, but he says: If I had wealth I would do what (the third man) did. He will be judged according to his intention, and their burden of sin will be the same.
Narrated by at-Tirmidhi, 2325; he said: this is a saheeh hasan hadeeth. Also narrated by Ibn Maajah, 4228
This questioner also has to pay attention to the fact that he may not be able to repent because of being overwhelmed by his whims and desires, his regarding sin as permissible and his persisting in it. He may not be able to do that because his time has come and his soul is taken. Let him listen to the words of Allah, may He be glorified and exalted (interpretation of the meaning):
And We shall turn their hearts and their eyes away (from guidance), as they refused to believe therein for the first time, and We shall leave them in their trespass to wander blindly
Ibn al-Qayyim (may Allah have mercy on him) said:
This is part of greater understanding: that a man fears that his sins may cause him misfortune at the time of death and keep him from a good end. Imam Ahmad narrated from Abu'd-Darda' that when he was dying, he would lose consciousness then he would come to and recite: And We shall turn their hearts and their eyes away (from guidance), as they refused to believe therein for the first time, and We shall leave them in their trespass to wander blindly
Because of that, the early generation feared sins, lest they kept them from a good end.
End quote from al-Jawaab al-Kaafi by Ibn al-Qayyim, 167
This questioner has to ask his Lord for forgiveness and repent to Him for having said this and having resolved to commit sin and persist in it. Allah, may He be glorified and exalted, has enjoined repentance upon His slaves. He says (interpretation of the meaning):
O you who believe! Turn to Allah with sincere repentance! It may be that your Lord will remit from you your sins, and admit you into Gardens under which rivers flow (Paradise)
Allah, may He be exalted, has told us that He accepts repentance from His slaves and that He will pardon them; indeed He will turn their bad deeds into good deeds. Allah says (interpretation of the meaning):
And He it is Who accepts repentance from His slaves, and forgives sins, and He knows what you do
Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allaah will change their sins into good deeds, and Allaah is Oft‑Forgiving, Most Merciful
Sincere repentance, according to the scholars, is that which fulfils the following conditions:
(a) Sincerity in repentance
(b) Giving up the sin
(c) Regretting the sin
(d) Resolving not to go back to the sin
(e) Repenting in time, for Allah does not accept repentance when the death rattle sounds before the soul is taken, or after the sun rises from its place of setting
(f) Restoring people's rights if the sin had to do with the rights of other people
We give our brother the glad tidings that if he has not done what he intended and spoke of, and he refrained from that out of fear of Allah and respect for His sacred limits, then Allah, may He be exalted, will record one good deed in his record, instead of the bad deed that he was thinking of doing.
It was narrated from Abu Hurayrah that the Messenger of Allah (blessings and peace of Allah be upon him) said: Allah says: If My slave thinks of doing a bad deed then do not write it down for him unless he does it, then if he does it write it down as one bad deed. And if he refrains from it for My sake, write down one good deed for him. If he wants to do a good deed then he does not do it, write it down as one good deed and if he does it, write it down tenfold up to seven hundred fold.
Narrated by al-Bukhaari, 7026; Muslim, 129.
And Allah knows best.
Reproduced from Islam QA