when did patient 9294 receive a prescription for nadolol in this month first?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 9294 ) and prescriptions.drug = 'nadolol' and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-0 month') order by prescriptions.startdate asc limit 1