I wanted to ask, is one thinking that he is for sure going to heaven bad or a sin? I remembering reading a Hadith, that said, having certitude that going to Heaven is bad, and I was just watching a lecture, and a Sayyed said, we should have certainty in Allah (SWT) and that we’re going to heaven.

So I was a bit confused, and wanted to know which of them is correct.

From our acts, we can know where we are going. Unless we repent and return to God, and with our adherence to the mandate of the Prophet and his pure family, and their intercession, then we hope to enter Paradise.