Is it wrong to use the word "Ya" (O) in supplication to Allah Almighty, as in saying "Ya Allah" (O Allah) or "Ya Rabb" (O Lord), based on the understanding that this word is used for a superior addressing an inferior, and because the Holy Quran only mentioned "Ya Rabb" (O Lord) twice in supplication, and both instances were complaints and not prayers? If that is the case, then how should we address Allah in supplication?

The Quran came with teachings on the etiquette of supplication, among which is the omission of the vocative particle "ya" (O) in a servant's supplication to his Lord, to signify the closeness of the One being called. In contrast, Allah uses "ya" when calling His servants, due to His transcendence and His independence from His creation. This omission of the vocative particle "ya" does not mean that its use is incorrect, as many Sunnahs and narrations indicate the permissibility of using the vocative particle "ya" in supplication to Allah Almighty, as seen in the supplications of the Prophets and Companions. Furthermore, the use of "ya" by the small to the great is not an error, for Noah and Abraham (peace be upon them) addressed their Lord with "O Lord," and Joseph and his brothers used "ya" in their address.

As for the difference between "Allahumma" and "Ya Allah," there is no difference in meaning. The preponderant view is that "Allahumma" is "Ya Allah" with the vocative particle omitted and replaced by a doubled "meem." The more common usage in supplication is "Allahumma" without "ya."