validate: if additional salary exists (#17529)

diff --git a/erpnext/hr/doctype/additional_salary/additional_salary.py b/erpnext/hr/doctype/additional_salary/additional_salary.py
index 9ca1260..043f0df 100644
--- a/erpnext/hr/doctype/additional_salary/additional_salary.py
+++ b/erpnext/hr/doctype/additional_salary/additional_salary.py
@@ -9,6 +9,12 @@
 from frappe.utils import getdate, date_diff
 
 class AdditionalSalary(Document):
+	def before_insert(self):
+		if frappe.db.exists("Additional Salary", {"employee": self.employee, "salary_component": self.salary_component,
+			"amount": self.amount, "payroll_date": self.payroll_date, "company": self.company}):
+
+			frappe.throw(_("Additional Salary Component Exists."))
+
 	def validate(self):
 		self.validate_dates()
 		if self.amount < 0: