- Remembrance of Allah
Ibn-Abbas said that the "days well-known" are the first ten days of Dhul-Hijjah while the "prescribed number of days" are the Days of Tashriq (11th, 12th and 13th of Dhul-Hijjah). Ibn-Omar and Abu-Hurairah used to go to the marketplace reciting takbir (saying: "Allahu Akbar [Allah is the Greatest]") and people followed their example.لِّيَشْهَدُوا مَنَافِعَ لَهُمْ وَيَذْكُرُوا اسْمَ اللَّهِ فِي أَيَّامٍ مَّعْلُومَاتٍ
"That they may witness (things) profitable to them and mention the Name of Allah on days well-known.”
(Al-Hajj, Chapter 22, Verse 28)
Prophet Mohammed وَسُلَمَ عًليهِ اللَّه صْلى said, "The best thing Allah likes is supplication."
(Related by at-Tirmithy and ranked as hadith hasan by al-Albany)