The Prophet ﷺ said: "There are no days in which righteous deeds are more beloved to Allah than these ten days."
They said: "Not even Jihad for the sake of Allah?"
He said: "Not even Jihad, except a man who goes out with his life and wealth and returns with nothing."
Bukhari: 969 | Tirmidhi: 757 | Musnad Ahmad: 1968
Scholars include Dhikr (Takbeer, Tahleel, etc.) as part of these righteous deeds.
Most common Takbeer to recite :
اللَّهُ أَكْبَرُ، اللَّهُ أَكْبَرُ، اللَّهُ أَكْبَرُ، لَا إِلَـٰهَ إِلَّا اللَّهُ، وَاللَّهُ أَكْبَرُ، اللَّهُ أَكْبَرُ وَلِلَّهِ الْحَمْدُ
1. Takbeerul Mutlaq (unrestricted) - Can be recited at any time from Maghrib of the 1st of Dhul-Hijjah to the 13th Dhul-Hijjah (before Maghrib)
2. Takbeerul Muqayyad (restricted) - Should be recited after every Fardh salaah starting from Fajr on the 9th of Dhul-Hijjah (Arafah) till Asr on the 13th. (Totals to 23 Fardh salaat)