It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "There are no days greater in the sight of Allah, nor are righteous deeds more beloved to Him in any days than in the ten days of Dhul-Hijjah, so increase in them the saying of Tahleel, Takbeer, and Tahmeed."