We were traveling with Allah's Messenger (ﷺ) and he was fasting, and when the sun set, he said to
(someone), "Get down and mix Sawiq with water for us." He replied, "O Allah's Messenger (ﷺ)! (Will you
wait) till it is evening?" The Prophet (ﷺ) again said, "Get down and mix Sawiq with water for us." He
replied, "O Allah's Messenger (ﷺ)! It is still daytime." The Prophet (ﷺ) said again, "Get down and mix Sawiq
with water for us." So, he got down and carried out that order. The Prophet (ﷺ) then said, "When you see
night falling from this side, the fasting person should break his fast," and he beckoned with his finger
towards the east.
Sahih al-Bukhari Book 30, Hadith 63