Hawt al-Abdi narrates: I asked Sayyiduna Zayd bin Arqam (may Allah be pleased with him) about the Night of Decree (Laylat al-Qadr), and he said: "I have no doubt and no hesitation that it is the night of the seventeenth (of Ramadan), the very night in which the Qur'an was revealed, and the very day on which the two armies met."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5060