Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates: We mentioned the Night of Qadr in the presence of the Prophet (peace and blessings be upon him), so the Prophet (peace and blessings be upon him) said: How much of the month has passed? We replied: Twenty-two (22) days have passed and eight days remain. The Prophet (peace and blessings be upon him) said: No, rather twenty-two (22) days have passed and seven days remain; sometimes the month is of twenty-nine (29) days, so seek this night.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2548
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح أبي داود» (2008).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرطهما