The first ten days of Dhul-Hijjah are venerated days. Allah takes an oath by them in the Qur-aan, and swearing by a thing is indicative of its importance and great benefit. Allah says (interpretation of the meaning):
“By the dawn;
By the ten nights (i.e. the first ten days of the month of Dhul-Hijjah)”
[al-Fajr 89:1]Ibn ‘Abbaas, Ibn al-Zubayr (RadiyAllaahu ‘anhum), Mujaahid (rahimahullaah) and others among the earlier and later generations said: This refers to the ten days of Dhu’l-Hijjah. Ibn Katheer (rahimahullaah) said: This is the correct view. [Tafseer Ibn Katheer, 8/413].
Good deeds during these days are beloved to Allah, because Rasoolullaah (Sallallaahu ‘Alayhi wa Sallam) said: “There are no days in which righteous deeds are more beloved to Allaah than these ten days.” They said, “O Messenger of Allaah, not even jihaad for the sake of Allaah?” The Messenger of Allaah (Sallallaahu ‘Alayhi wa Sallam) said, “Not even jihaad for the sake of Allah, except in the case of a man who went out to fight, giving himself and his wealth up for the cause, and came back with nothing.” [Bukhaari, 969; al-Tirmidhi, 757. This version was narrated by al-Tirmidhi and classed as saheeh by al-Albaani in Saheeh al-Tirmidhi, 605].
One of the righteous deeds during these days is to remember Allah by reciting Takbeer (saying “Allaahu akbar”) and Tahleel (saying “Laa ilaaha ill-Allaah”), because of the following evidence.
1. Allah says (interpretation of the meaning): “That they may witness things that are of benefit to them (i.e. reward of Hajj in the Hereafter, and also some worldly gain from trade), and mention the Name of Allaah on appointed days”. [Surah 22/al-Hajj, v:28]
The “appointed days” are the first ten days of Dhul-Hijjah.
2. Allaah says (interpretation of the meaning): “And remember Allaah during the appointed Days”. [Surah 02/al-Baqarah, v:203]
These are the days of al-Tashreeq, i.e. the 11th, 12th and 13th of Dhul-Hijjah.
Recite:
Allaahu akbar, Allaahu akbar, Allaahu akbar, laa ilaaha ill-Allaah, Allaahu akbar, Allaahu akbar, Allaahu akbar, wa lillaahi’l-hamd
Meaning:
Allaah is Most Great, Allaah is Most Great, Allaah is Most Great, there is no god but Allaah, Allaah is Most Great, Allaah is Most Great, Allaah is Most Great, and to Allaah be praise.
or
Allaahu akbar, Allaahu akbar, Allaahu akbar, laa ilaaha ill-Allaah, Allaahu akbar, Allaahu akbar, wa lillaahi’l-hamd
Meaning:
Allaah is Most Great, Allaah is Most Great, Allaah is Most Great, there is no god but Allaah, Allaah is Most Great, Allaah is Most Great, and to Allaah be praise.
The matter is broad in scope because there is no text narrated from the Prophet SAW which specifies a particular form of the Takbeer.
Shaykh Salih al Munajjid