Paying salary into an employees pension

We have a worker who has asked if we could pay a large amount (£5,000) of their weekly earnings into their personal pension. They have asked that £1,000 of this be deducted as a salary sacrifice and the remaining £4,000 be paid into the pension as an employer contribution. I have found lots of conflicting advice online about whether this is possible or not and wanted to get a definitive answer before going back to the worker. Thank you

Hi

When an employee enters into a salary sacrifice agreement, they give up the right to the money and any subsequent contribution into a pension scheme would always be an employer contribution. 
There is information at Salary sacrifice for employers.
I would also advise calling the Employer Helpline on 0300 200 3200 for more information as it is not clear exactly what your employee is looking to salary sacrifice and the tax/NIC implications.  

Thank you