Sometimes in my heart I say things I don't want to say.
Is Allah going to hold me accountable for these?
What can we do about bad/illicit thoughts striking our heart?
ALLAH will never ask you about something you never do.
عن أبي عبد الله الصادق(ع): "إنّ المؤمن ليهمّ بالحسنة ولا يعمل بها فتكتب له حسنة، وإنْ هو عملها كتبت له عشر حسنات، وإن المؤمن ليهمّ بالسيئة أن يعملها فلا يعملها فلا تكتب عليه" (الكافي ج2 ص429)
Abu Abdullah al-Sadiq (AS): "The believer does not matter with good works is recorded him well, and that is the work wrote him ten good deeds, although the insurer to matter as bad that he does not he does not write it" (AlKafi part2 page429)
ALLAH will ask you for your acts, also will ask you for speaks if those words hurt others or yourself like backbiting, fading, bad words...
Many people can be affected by bad/illicit thoughts and temptations and you're not alone in that.
We should remember that the conditions of our heart (desires, temptations, thoughts etc.) do indeed influence the way we think and act. Its through our heart that we are tempted to do sins. Allah says in Surah an-Naas:
Say, “I seek refuge in the Lord of mankind. The King of mankind. The God of mankind.From the evil of the sneaky whisperer. Who whispers into the hearts of people. From among jinn and among people.” (114)
In another verse Allah says that our actions are dictated by our psychological structure:
Say: Every one acts according to his shakilah (his psychological structure); but your Lord best knows who is best guided in the path. (17:184)
And that in addition to our deeds, our heartfelt desires do have a role in shaping our eternal fate. Sheikh Tusi (a 12th century Shiite scholar) narrates from the Holy Prophet:
O Abadhar! Indeed, Allah doesn't look at your appearances and your possessions, but He looks at your hearts and your deeds. (Amali: p. 536)
Therefore, it is necessary to have a strategy to remove any negative conditions from our heart permanently before they become part of our internal structure and influence us. So here's a comprehensive strategy that I have come up with to permanently eliminate bad/sinful/negative thoughts from our hearts:
In the short run:
In the long run:
Indeed, those who fear Allah - when an impulse touches them from Satan, they remember [Him] and at once they have insight. http://tanzil.net/#7:201
Whoever comes [on the Day of Judgement] with a good deed will have ten times the like thereof [to his credit], and whoever comes with an evil deed will not be recompensed except the like thereof; and they will not be wronged. http://tanzil.net/#6:160
Evil deed has punishment. And think of evil deed does not have punishment.
Thinking of sin and committing sin are different. Think of sin has no punishment but still it has bad effects on soul. It makes the heart (soul) dirty. Committing sin is like fire in home that burns home. And think of sin it is like black smoke inside home that does not burn home but makes it dirty.
According to first verse the duty of Muslims who have Taqwa is to remember God and having insight.