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 saying Tahleel, Takbeer, and Tahmeed during these days.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6154
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لضعف يزيد بن أبى زياد .