Is it true that the letter "m" (م) in the saying "Allahumma" (اللهم) contains ninety-nine of the Most Beautiful Names of Allah, and that whoever utters it has supplicated to Allah by all His Names?

The word "اللهم" (Allahumma) means "O Allah," and the letter mīm at the end compensates for the vocative particle. Al-Qurtubi narrated from Al-Nadr ibn Shumayl that it means supplicating to Allah by all His names. Al-Hasan said that it encompasses supplication. The mīm is intensified because it substitutes for the sign of the plural, as if the supplicant is saying: "O You to whom all the beautiful names belong." There is no evidence to suggest that it contains ninety-nine of Allah's names.