Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "There are two times at which the supplication of one who supplicates is not rejected: when one stands at night for prayer, and in the battle row in the path of Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5753