Buhari congratulates mohammed salman on his appointment as saudi pm

I apologize, but it seems you've provided incorrect information. There is no record of Nigerian President Muhammadu Buhari congratulating Mohammed Salman on his appointment as Saudi PM.

Mohammed bin Salman (MBS) has been the Crown Prince of Saudi Arabia since 2017 and has been serving as the Deputy Prime Minister and Minister of Defense since 2015. He has not been appointed as the Prime Minister of Saudi Arabia.

It's possible that you may be thinking of a different person or event. If you could provide more context or clarify what you're referring to, I'll be happy to help.