Sayyiduna al-Nu'man bin Muqarrin (may Allah be pleased with him) says: I used to be present with the Messenger of Allah (peace and blessings be upon him); if he (peace and blessings be upon him) did not fight in the early part of the day, he would postpone it until the sun had declined, the winds blew, and help descended.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18465