The Prophet ﷺ said, "There are no days greater in the sight of Allah, nor any in which deeds are more beloved to Him, than these days," meaning the ten days of Dhul-Hijjah, "so increase in them the saying of La ilaha illa Allah and al-Humayd lillah."
عن النبي ﷺ قال: قال رسول الله ﷺ: ما من أيام أعظم عند الله، ولا العمل فيهن أحب إلى الله من هذه الأيام، فأكثروا فيها التهليل والتحميد يعني أيام العشر.
Abu Awana narrated it in his Musnad (3024), from Abu Yahya Abdullah bin Ahmad bin Abu Maysara, who said, "Abdul-Hameed bin Ghazwan Basri narrated to us, Abu Awana narrated to us, from Musa bin Abu Ayesha, from Mujahid, from Ibn Abbas," and he related it. Its chain is sahih, and Musa bin Abu Ayesha is trustworthy, one of the men accepted by the whole community of scholars.Imam Ahmad (5446) and Abd bin Humayd (807) both narrated it from the hadith of Abu Awana, who said, "Yazid bin Abu Ziyad narrated to us, from Mujahid," with the same wording. Yazid bin Abu Ziyad is the Hashimi client, and he is daif, but he is corroborated in the first chain.