Sh. Ibn al-‘Uthaymeen Raḥimahullāh said: 
“And strange is that people are unaware of (the virtue of) ten days of Dhul-Ḥijjah, 
you will see them striving in the last 10 days of Ramaḍān with good deeds but during Dhul-Ḥijjah you would find ALMOST NONE of them making any difference between these virtues 10 days and other normal days (i.e he does not make any special effort for Dhul-Ḥijjah).”
● [مجموع فتاوى الشيخ محمد بن صالح العثيمين ، مجلد ٢١ ، صفحة ٣٧]