Human instinct particularly in Europe is that human mind is free. My question is: I have heard someone insult God with words that are so nasty that they are shown with a beep in media. Am I allowed to remember his voice when he insulted God? For example: I am staying idle and I remember a conversation I had with shaik assim. Similarly I remember the voice that insulted God. Is this kufr or sinful?
There aren't any kufr or sinful in remembering and thinking, but also you shouldn't think such memories. Such things are delusion of devil. If you have many of delusions you should say kalimai tawheed many of times in day.