Sahih Bukhari

Narrated Ibn Abi `Aufa:I was with the Prophet (ﷺ) on a journey, and he observed the fast till evening. The Prophet (ﷺ) said to a man, ""Get down and mix Sawiq with water for me."" He replied, ""Will you wait till it is evening?"" The Prophet said, ""Get down and mix Sawiq with water for me; when you see night falling from this side, the fasting person should break his fast