Sunan Ibn Majah, Hadith 1691 ⓘ
It was narrated from Abu Hurairah that the Messenger of Allah said: “When anyone of you is fasting, let him not utter evil or ignorant speech. If anyone speaks to him in an ignorant manner, let him say: ‘I am fasting.’”
حَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ، أَنْبَأَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ فَلاَ يَرْفُثْ وَلاَ يَجْهَلْ فَإِنْ جَهِلَ عَلَيْهِ أَحَدٌ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ " .
also referenced under: Book 7, Hadith 1761 (In-Book) & Volume 2, Book 7, Hadith 1691 (DarusSalam)