Code 1:

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
<!-- Sequence for sale orders in quotation state -->
<record id="seq_sale_order_quotation" model="ir.sequence">
<field name="name">Sale Order Quotation</field>
<field name="code">sale.order.quotation</field>
<field name="prefix">QU</field>
<field name="padding">5</field>
<field name="company_id" eval="False"/>
</record>
</odoo>

Code 2:

# -*- coding: utf-8 -*-

from odoo import api, fields, models

class SaleOrder(models.Model):
"""Inherit sale order for custom Sequence"""
_inherit = "sale.order"

@api.model_create_multi
def create(self, vals_list):
for vals in vals_list:
if vals.get('state', 'draft') == 'draft':
vals['name'] = self.env['ir.sequence'].next_by_code('sale.order.quotation')
return super(SaleOrder, self).create(vals_list)

def action_confirm(self):
res = super(SaleOrder, self).action_confirm()
for order in self:
if order.state == 'sale':
order.name = self.env['ir.sequence'].next_by_code('sale.order')
return res

def action_draft(self):
for order in self:
if order.write({'state' : 'draft'}):
order.name = self.env['ir.sequence'].next_by_code('sale.order.quotation')
res = super(SaleOrder, self).action_draft()
return res