The most common and most likely answer to this crossword clue is the 4 letter word IMAM
I've seen this crossword clue in Financial Times
I
M
A
M
More clues leading to the result IMAM
- Prayer leader? I am a medium
- One that gets muezzin going in the morning
- I’m holding mass as prayer leader
- Monk initially entering an hour after midnight as man of prayer
- Announcement of PM’s successor as Muslim leader
- This writer's a male religious leader
- Prayer an hour after midnight inspiring music, initially
- Second in race, in a short distance, becomes leader
- Mosque officer? Don’t give —— for ’is supper!
- I’m a leader of Muslims
Buddy explains!

The straight part
We know that "I’m a leader of Muslims" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i’m a leader of muslims = imam.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IMAM mean?
IMAM noun- (usually capitalized) A Shi'ite Muslim leader.
- One who leads the salat prayers in a mosque.