There is practically no difference between saying, “Sadaqa Allahu Al-Adheem” (Allah the Most Great spoke the truth) or “Sadaqa Allahu Al-’Ali Al-Adheem” (Allah the Most Great and Most High spoke the truth). This issue is perhaps the least significant between the schools of thought, especially since both sayings have been used occasionally in both, the Shi‘a and the Sunni schools of thought.
However, the source of saying either of the above mentioned will be referred to the Noble Qur’an to dispel any misconceptions which may arise in the minds of some Muslims who think that the word “Al-’Ali” refers to Imam ‘Ali ibn Abi Talib, though it does not.
The initial phrase “sadaqa allah” occurs in the Qur’an in many places such as, “Say: Allah has spoken the truth (sadaqa Allah).” “Al-’Ali” and “Al-Adheem” are among the 99 attributes of Allah. In the Noble Qur’an, Allah mentions His name coupled with “al-Adheem” by itself once, and He mentions both attributes together twice (2:255 and 42:4) whereas “Al-’Ali,” which is mentioned in numerous verses, such as 22:62, 31:30, 34:23, 40:12, 4:34, 42:51, not to mention others. Therefore, mentioning both attributes together (“Al-’Ali” and “Al-Adheem”) is in no way a reference to the name of Imam ‘Ali but rather imitating what the Noble Qur’an says in glorifying and exalting Almighty Allah.
 Noble Quran 3:95
 Noble Quran 69:33