The meaning of the sincere repentance

I asked Abu’l-Hasan, the Last, peace be upon him, about the sincere repentance: What is it? So he, peace be upon him, wrote: That the internal is like the apparent and (even) better than that.

It is the fasting of the day of Wednesday, the day of Thursday and the day of Friday.

the sincere repentance is that a man repents from a sin and intends to not return to it.