✅Answer: Please pay attention to the following narrations:

1 مُحَمَّدُ بْنُ عَلِيِّ بْنِ الْحُسَيْنِ بِإِسْنَادِهِ عَنْ زُرَارَةَ قَالَ سَمِعْتُ أَبَا جَعْفَرٍ يَقُولُ الدُّعَاءُ بَعْدَ الْفَرِيضَةِ أَفْضَلُ مِنَ الصَّلَاةِ تَنَفُّلًا فَبِذَلِكَ جَرَتِ السُّنَّةُ

📚Faqih, Vol. 1, p. 328

Translation: Zurarah said: I heard Imam Baqir (peace be upon him) say: 'Supplication after an obligatory prayer is better than a supererogatory prayer, so the tradition has been established on this.'

2 عَنْ حَمَّادِ بْنِ عِيسَى عَنْ عُبَيْدِ بْنِ زُرَارَةَ عَنْ أَبِي عَبْدِ اللَّهِ أَنَّهُ سَأَلَهُ عَنْ رَجُلَيْنِ قَامَ أَحَدُهُمَا يُصَلِّي حَتَّى أَصْبَحَ وَ الْآخَرُ جَالِسٌ يَدْعُو أَيُّهُمَا أَفْضَلُ قَالَ الدُّعَاءُ أَفْضَلُ.

📚Tahdhib, Vol. 4, p. 331

Translation: 'Ubayd ibn Zurarah asked Imam Sadiq (peace be upon him) about two people, one of whom stands and prays until morning, and the other who sits and supplicates: 'Which of them is more virtuous and better?' The Imam said: 'Supplication is more virtuous.'

✅It is clear from the two above narrations that, after an obligatory prayer, performing 'ta'qibat' and supplication is more virtuous than performing a supererogatory prayer. Of course, such comparisons, which have been mentioned in narrations for various matters, do not mean abandoning the less virtuous act. For example, in narrations, visiting Imam Husayn (peace be upon him) is given virtue over Hajj, and this does not mean abandoning Hajj. In the case of the question as well, supplication after an obligatory prayer is given superiority over performing a supererogatory prayer, and the intention is to mention the superiority and preference, not to abandon the supererogatory prayer.

✅Also, pay attention to the following two narrations:

3 عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ صَفْوَانَ عَنِ الْعَلَاءِ بْنِ رَزِينٍ عَنْ مُحَمَّدِ بْنِ مُسْلِمٍ عَنْ أَحَدِهِمَا قَالَ: الدُّعَاءُ دُبُرَ الْمَكْتُوبَةِ أَفْضَلُ مِنَ الدُّعَاءِ دُبُرَ التَّطَوُّعِ كَفَضْلِ الْمَكْتُوبَةِ عَلَى التَّطَوُّعِ.

📚Tahdhib, Vol. 4, p. 104

Translation: Imam Sadiq or Imam Baqir (peace be upon them) said: 'The superiority of supplication after an obligatory prayer over supplication after a supererogatory prayer is like the superiority of an obligatory prayer over a supererogatory prayer.'

4 عَنْ أَبَانِ بْنِ عُثْمَانَ عَنِ الْحَسَنِ بْنِ الْمُغِيرَةِ أَنَّهُ سَمِعَ أَبَا عَبْدِ اللَّهِ يَقُولُ إِنَّ فَضْلَ الدُّعَاءِ بَعْدَ الْفَرِيضَةِ عَلَى الدُّعَاءِ بَعْدَ النَّافِلَةِ كَفَضْلِ الْفَرِيضَةِ عَلَى النَّافِلَةِ

📚Kafi, Vol. 3, p. 341

Translation: Hasan ibn Mughirah heard Imam Sadiq (peace be upon him) say: 'Indeed, the virtue and superiority of supplication after an obligatory prayer over supplication after a supererogatory prayer is like the virtue of an obligatory prayer over a supererogatory prayer.'

✅It is also clear from these two above narrations that supplicating after an obligatory prayer has a superiority over supplicating after a supererogatory prayer, to the extent of the superiority of the obligatory prayer over the supererogatory prayer. One of the places to use these narrations is, for example, to perform the 'ta'qibat' of the Maghrib prayer after the Maghrib prayer, not after its supererogatory prayers, because according to the above narration, this act has more virtue.

✅In several narrations, in general, supplication has been introduced as the most virtuous of deeds and the most firm of worships.

The superiority of supplication after an obligatory prayer over a supererogatory prayer