Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that some men from among the Companions of the Prophet (peace and blessings be upon him) were shown in their sleep that Laylat al-Qadr is in the last seven (nights) of Ramadan. So the Messenger of Allah (peace and blessings be upon him) said: "I hear that your dreams have agreed that it is in the last seven; so whoever would seek it, let him seek it in the last seven."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8544