Zirr bin Hubaysh (may Allah have mercy on him) narrates: I asked Ubayy bin Ka'b (may Allah be pleased with him) about Laylat al-Qadr, and he swore that it is the twenty-seventh night. I said: How do you say that, O Abu al-Mundhir? He said: Because of the signs and indications which the Prophet (peace and blessings be upon him) described, for he (peace and blessings be upon him) said: "On the morning of that day the sun rises without rays."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8551