Sayyiduna Utbah bin Ghazwan (may Allah be pleased with him) said: We used to take part in battle with the Messenger of Allah (peace and blessings be upon him). When the sun passed its zenith, he (peace and blessings be upon him) would say to us: "Charge!" So we would charge.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14359