✅ Answer: Please consider the following narration:

1⃣عَنْ مُحَمَّدِ بْنِ یَحْیَی عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ مُحَمَّدِ بْنِ إِسْمَاعِیلَ عَنْ مُحَمَّدِ بْنِ الْفُضَیْلِ عَنْ أَبِی الصَّبَّاحِ الْکِنَانِیِّ قَالَ سَأَلْتُ أَبَا عَبْدِ اللَّهِ عَنْ رَجُلٍ عَلَیْهِ مِنْ شَهْرِ رَمَضَانَ أَیَّامٌ أَ یَتَطَوَّعُ فَقَالَ لَا حَتَّی یَقْضِیَ مَا عَلَیْهِ مِنْ شَهْرِ رَمَضَانَ

📚 *Kafi*, Vol. 4, p. 123

Translation: Abu Sabah Kanani said: I asked Imam al-Sadiq (AS): Can someone who has missed days of fasting from Ramadan fast a voluntary fast? Imam replied: No, not until they have completed all the missed fasts of Ramadan!

✅ According to this narration and the narrations in Chapter 28 of *Wasa'il al-Shi'a*, Vol. 7, regarding the rulings of the month of Ramadan, a person who has obligatory fasts (qadha) to make up is not allowed to fast a voluntary (mustahabb) fast until they complete their obligatory fasts.

اللَّهُمَّ فَصَلِّ عَلَی مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ عَجِّلْ لِوَلِیِّکَ الْفَرَجَ وَ الْعَافِیَةَ وَ النَّصْرَ