What a fasting person should say if someone insults him

اِنِّيْ صَآئِمٌ ، اِنِّيْ صَآئِمٌ

Indeed, I am fasting. Indeed, I am fasting.

1. Sahih al-Bukhari, no. (1894), Sahih Muslim, no. (1151), the wording is his, Sunan Abi Dawud, no. (2363).