Sayyiduna Anas bin Malik (may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings be upon him) fought a people, he would not attack before morning. If he heard the call to prayer (adhan), he would refrain from attacking, and if he did not hear the call to prayer, he would attack after morning had come.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18237