Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "The calendar (the Hijri calendar) began from the very year in which the Prophet (peace and blessings be upon him) came to Madinah, and in that same year Abdullah bin al-Zubayr (may Allah be pleased with them both) was born."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11136