Mishkat al-Masabih 7 Fasting كتاب الصوم 62

وَعَن عَطاء قَالَ: إِن مضمض ثُمَّ أَفْرَغَ مَا فِي فِيهِ مِنَ الْمَاءِ لَا يضيره أَنْ يَزْدَرِدَ رِيقَهُ وَمَا بَقِيَ فِي فِيهِ وَلَا يَمْضُغُ الْعِلْكَ فَإِنِ ازْدَرَدَ رِيقَ الْعِلْكَ لَا أَقُولُ: إِنَّهُ يُفْطِرُ وَلَكِنْ يُنْهَى عَنْهُ. رَوَاهُ الْبُخَارِيُّ فِي تَرْجَمَةِ بَابٍ

‘Ata’ said, “If one rinses his mouth and ejects the water in it, swallowing his saliva and anything that remains in it does him no harm; but one should not chew gum, for although I do not say that he breaks his fast [if] he swallows the saliva produced by the gum, he is nevertheless prohibited from doing it.” Bukhari transmitted it in a chapter heading.