Musnad al-Humaydi

Zirr bin Hubaish says: I said to Sayyiduna Ubayy (may Allah be pleased with him): Your brother, Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), says: Whoever performs voluntary prayers throughout the year, only he can attain Laylat al-Qadr. So Sayyiduna Ubayy (may Allah be pleased with him) said: May Allah have mercy on Abu Abdur Rahman; his intention is that people should not rely on (any one specific night) and become complacent, otherwise he also knows that it is in the last ten nights of Ramadan, and it is the twenty-seventh night. Then Sayyiduna Ubayy (may Allah be pleased with him) swore an oath without any exception and stated that it is the twenty-seventh night. We requested him: O Abu al-Mundhir! How did you come to know this? He replied: Because of the sign (the narrator is in doubt, perhaps these are the words) or the indication about which the Prophet Muhammad (peace and blessings be upon him) informed us. The Prophet Muhammad (peace and blessings be upon him) informed us that "on the morning following that night, when the sun rises, it has no rays."