In Task creation for Opportunity I have to make sure that only certain picklist values are available (or we can restrict to Save Task from Valiation Rule on Task) in Custom Pricklist field for certain Stage field values in Opportunity.Now, from Task in Validation Rule we can get only Parent ID (WhatID) which will be ID of Opportunity.Now, how I can get Stage field of Opportunity in Validation Rule.I want something like:If (WhatId.Stage = '4 Handover', Category__c!='Order', false)