In which month Hazrat Muhammad (S.A.W) and Hazrat Khadija (R.A) got married?

Salam to everyone.. I am asking this question because, by looking at this question this question is looks very easy but is very difficult in real. In which month Hazrat Muhammad (S.A.W) and Hazrat Khadija (R.A) got married? Yesterday, we were having conversation in our home and someone suddenly asks this question and no one was able to answer this. I don't know if someone will find it easy to answer but for me this question is very difficult. Is there any reference in QURAN about their marriage ? Jazakallah .