Takbeer Tashreeq is the recitation of "Allaahu akbar, La ilaaha [illa Allaahu] Wallaahu akbar, Allaahu akbar wa lillaahil hamd" after every fardh salaah commencing from the Fajr of the 9th of Dhul Hijah until after Asr of the 13th of Dhul Hijjah. (Shami vol. 1 pg. 406)

When Ibrahim (AS) began moving the knife on his beloved son, Ismaeel (AS), the angels sent by Allah with a ram exclaimed, "Allahu akbar, Allahu akbar (Allah is the greatest, Allah is the greatest)."

Ibrahim (AS) heard the voice of the angels and replied, "La illaah illa Allaahu Wallaahu akbar (There is no god besides Allah, and Allah is the greatest)."

His son Ismaeel (AS) heard this conversation and understood that Allah had relieved him from this great trial, thus he replied, "Allaahu Akbar Wa lillaahil hamd (Allah is the greatest, and to Allah belongs all praise)." (Ibid)

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai, www.ask-imam.com
FATWA DEPT.