Ibn ‘Abbas (RadiyAllahu Anhuma) says about the verse,
“Remember Allah during the well known days,”
(Noble Qur’an 22:28)
.. that it refers to the first ten days of Dhul-Hijjah.
[This is related by al-Bukhari]
Praise be to Allah Who has created Time and has made some times better than others, some months and days and nights better than others, when rewards are multiplied many times, as a mercy towards His slaves. This encourages them to do more righteous deeds and makes them more eager to worship Him, so that the Muslim renews his efforts to gain a greater share of reward, prepare himself for death and supply himself in readiness for the Day of Judgment.
This season of worship brings many benefits, such as the opportunity to correct ones faults and make up for any shortcomings or anything that one might have missed. Every one of these special occasions involves some kind of worship through which the slaves may draw closer to Allah, and some kind of blessing though which Allah bestows His favor and mercy upon whomsoever He will. The happy person is the one who makes the most of these special months, days and hours and draws nearer to his Lord during these times through acts of worship; he will most likely be touched by the blessing of Allah and will feel the joy of knowing that he is safe from the flames of Hell.
[Ibn Rajab, al-Lataif, p.8]
Ibn ‘Abbas (RadiyAllahu Anhuma) reports that the Messenger of Allah (SallAllahu Alayhi Wa Sallam) said,
“No good deeds done on other days are superior to those done on these days [meaning the ten days of Dhul-Hijjah].”
The companions asked, “O Messenger of Allah, not even jihad in the way of Allah?”
He said, “Not even jihad, except for the man who puts his life and wealth in danger [for Allah’s sake] and returns with neither of them.”
[This is related by the group except Muslim and an-Nasa’i]
Ahmad and at-Tabarani record from Ibn ‘Umar (RadiyAllahu Anhuma) that the Messenger of Allah (SallAllahu Alayhi Wa Sallam) said:
“There is no day more honorable in Allah’s sight and no acts more beloved therein to Allah than those in these ten days. So say tahlil (There is no deity worthy of worship but Allah: La ilaha ill Allah), takbir (Allah is the greatest: Allahu Akbar) and tahmid (All praise is due to Allah: alhumdulillah) a lot [on those days].”
[Reported by Ahmad, 7/224; Ahmad Shakir stated it is Sahih]