The Messenger of Allah ﷺ said, "Fasting is a shield. So when one of you is fasting for a day, let him not act foolishly or speak obscenely. And if a man fights him or insults him, let him say, 'I am fasting, I am fasting.'"
وقال رسول الله ﷺ الصيام جنة فإذا كان أحدكم يوما صائما فلا يجهل ولا يرفث فإن امرؤ قاتله أو شتمه فليقل إني صائم إني صائم
It is sahih based on the soundness of what precedes it in the manuscript, and it appears in the individual manuscript as number 15. The two Shaykhs (Bukhari and Muslim) did not narrate it through the manuscript's route, but they both narrated it, at length and in abridged form, through multiple routes. Among these, Bukhari narrated it in 88-91 Fath, combined with the following hadith as a single hadith, from the version of Araj. Muslim narrated only his saying, "Fasting is a shield," alone, in 316:1 Bulaq, from the version of Araj, then narrated it at length within a long hadith, from the route of Abu Salih from Abu Hurairah.This has already appeared repeatedly in the Musnad, at length and in abridged form, through many routes, and it will appear again repeatedly as well. Among these is its narration with this wording in 7484, from the route of Musa bin Yasar and Araj, from Abu Hurairah. Among these is its narration in similar wording with some abridgment in 7336, from the route of Araj. Among these is its narration within a long hadith in 7679, from the route of Abu Salih from Abu Hurairah. We have indicated there many of its routes in the Musnad.