Make Field Bussiness required on Qualify Lead

Hello

i have requirement when user qulify lead,the Lead Status = Contacted (Must be Contacted prior to Qualification)

• If Lead Status is New at time of Lead Qualification, present the  message to the user:You can't qualify this lead.

i have achieve this through plugin but after:

 abc(lookup) contains data (abc field is optional at Lead Save, but Required at Qualification)

i don't know how this i can implement.

Thanks in advance.