Hadith 4:634
Hafs narrated to us, from ‘Amr, from al-Hasan, who said: He used to fast it between himself and midday, due to the testimony of a witness or the arrival of someone absent. If he (the witness) came, (he would continue), and if not, he would break his fast.
حدثنا حفص عن عمرو عن الحسن قال كان يصومه فيما بينه وبين نصف النهار لشهادة شاهد أو مجيء غائب فإن جاء وإلا أفطر