Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) narrates: The Prophet Muhammad (peace and blessings be upon him) separated himself from his wives for a month. On the morning of the twenty-ninth day, the Prophet (peace and blessings be upon him) came, so one of those present said: O Messenger of Allah (peace and blessings be upon him)! It has only been twenty-nine days. The Prophet (peace and blessings be upon him) said: A month can also be of twenty-nine days. Then the Prophet (peace and blessings be upon him) indicated three times with all the fingers of both hands, and on the third time, he indicated with nine fingers (i.e., a month can also be of twenty-nine days).
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3452
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الصحيحة» (3505): م.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرطهما