Can the fast of missed days of Ramadan be observed on Saturdays?

My situation is that during week days I am not able to fast because my work extends until the time of sun set (so I don't have time to break the fast), and on Saturdays I am free and I find it easy to fast. But I heard a Hadith that Prophet Muhammad (salallahu alaihi wasallam) has made it forbidden to fast on Saturdays except during the month of Ramadan. What is the ruling in this case?

Fasting on Saturdays in your case would be permissible because you are doing a qadaa' fast which is an exception here. What is not allowed is a general nafil fast but, a compulsory or qadaa' fast is allowed.