It is narrated from Abu Darda (may Allah be pleased with him) that he would come to his family when half the day had passed or a little before that, and would say: "Is there any breakfast?" If there was or was not, he would say: "I will fast today," and then he would fast. If he was not fasting and came at that time, he would remain without fasting.
Hadith Referenceمسند الإمام الشافعي / كتاب الصيام / 642
Hadith Takhrijاسناده صحيح وعـنـعـنة ابن جريج عن عطاء مقبولة : اخرجه البيهقي في المعرفة السنن والآثار (2442) ۔ وعبد الرزاق (7776) وابن ابي شيبة (9106)، (9109)۔