Opening remark thanks young adult for boosting religious leader (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

HALLO (opening remark) + TA (short for “thank you” = thanks) + YA (young adult, especially in describing fiction written for teenagers), all reversed (boosting = lifting up = upwards in a down clue). Title for a Shia Muslim leader.