Al-Kāfi - Volume 4 > The Case of a Fasting Person’s Vomiting, Nauseating or Burping
Hadith #6

6ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عُثْمَانَ بْنِ عِيسَى عَنْ سَمَاعَةَ قَالَ سَأَلْتُهُ عَنِ الْقَلْسِ وَهِيَ الْجُشْأَةُ يَرْتَفِعُ الطَّعَامُ مِنْ جَوْفِ الرَّجُلِ مِنْ غَيْرِ أَنْ يَكُونَ تَقَيَّأَ وَهُوَ قَائِمٌ فِي الصَّلاةِ قَالَ لا يَنْقُضُ ذَلِكَ وُضُوءَهُ وَلا يَقْطَعُ صَلاتَهُ وَلا يُفَطِّرُ صِيَامَهُ.

6. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ‘Uthman ibn ‘Isa from Sama‘ah, who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about burping which is belching and brings food up from the inside of a man without vomiting and when he is standing in Salat (prayer). He (the Imam) said, ‘It does not invalidate his wudu’, destroy his Salat (prayer) or invalidate his fast.’”