Buhari warns that next four years will be tough

I'm not aware of any recent statement from President Muhammadu Buhari warning that the next four years will be tough. It's possible that you may be referring to a previous statement or a quote from an interview.

However, it's worth noting that President Buhari has faced several challenges during his tenure, including economic downturn, security issues, and corruption. He has also made efforts to address these challenges, including implementing policies to stimulate economic growth, improving security measures, and tackling corruption.

If you could provide more context or clarify which statement you are referring to, I may be able to help you better.