One has to complete the fasting of ramadan first and only then fast the 6 days of shawwal. It doesn’t have to be in a row.

I wanted to know if one can fast 6 fasts of shawaal before they have completed their fard ones I.e. the ones that they missed in Ramadan? Also, are the 6 fasts observed in a row or can be observed on alternate days

Fasting | July 25, 2014 4:01 pm
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In Jeddah/Makkah/Medinah the dawn start when the adhan is called or before? And is it permissible to drink whilst fajr adhan is going on?
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After completing ramalaan and celebrating eid festival, do we have to make six days fasting continuously or whenever we feel can we make that six days fasting randomly ????