What is the Ruling on Fasting in Shawwal before Making Up Missed Fasts from Ramadan?

The correct statement of the people of knowledge is that it is not permissible for a person to begin with a Nafl (voluntary worship) before he finishes his Fardh (obligation). Just as it is not permissible for a person to give voluntary charity while he is obligated to give Zakat, unless he has excess money. Likewise, it is not permissible for a person to give voluntary charity while someone is demanding the repayment of a debt from him. So, it is not correct for a person to do Nafl (voluntary) fasting while he has not yet made up the obligatory fasting yet. Therefore, we start with making up the obligatory fasts first, then fast the six days of Shawwal after that. If someone says, "if I make up my obligatory fasts then Shawwal may end before I can do them all, so how should I make them up?" We say: intend to make up the 6 fasts of Shawwal immediately after finishing the obligatory fasting, and Allah the Exalted knows best.