(21) CHAPTER. If the intention of observing Saum (fast) was made in the daytime…
Umm Ad-Darda’ said: Abu Ad-Darda’ used to ask, “Do you have food?” If we answered in the negative, he would say, “Then I am observing Saum (fasting) today.” Abu Talla, Abu Hurairah, Ibn ‘Abbãs and Hudhaifa did the same.
1924. Narrated Salama bin Al-Akwa’: Once the Prophet, peace be upon him, ordered a person on the day of Ashura (the tenth of Muharram) to announce, “Whoever has eaten, should not eat any more, but observe Saum (fast), and who has not eaten should not eat, but complete his Saum (fast) (till the end of the day).”