Sayyiduna Abu Bakrah (may Allah be pleased with him) narrates: The Noble Prophet (peace and blessings be upon him) said: The two months of Eid are not reduced—Ramadan and Dhu al-Hijjah. (Imam Ibn Hibban, may Allah have mercy on him, says:): This narration can have two meanings. One of them is: The two months of Eid are in reality not reduced, even though according to our sight they may appear to be less. This happens when there is dust or clouds or something similar that prevents us from sighting the moon. The second meaning is: The two months of Eid are not less in terms of virtue. This means: The first ten days of the month of Dhu al-Hijjah have the same status in terms of virtue as the month of Ramadan, and the evidence for this is the statement of the Noble Prophet (peace and blessings be upon him): "There are no days in which righteous deeds are more virtuous than the first ten days of Dhu al-Hijjah." It was asked: O Messenger of Allah! Not even striving in the way of Allah? The Noble Prophet (peace and blessings be upon him) said: Not even striving in the way of Allah.
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3448
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: ق - مضى (325).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates this statement of the Prophet Muhammad (peace and blessings be upon him): "A month (sometimes) consists of twenty-nine (29) days."
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3449
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: ق - وهو مختصر الآتي بعد حديث.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين