His message was conveyed in a statement by his Special Adviser on Media and Publicity, Femi Adesina, on Tuesday.
Adesina quoted the President as giving glory to God for the gift of long life and sound mind bestowed on the Niger Delta Leader.
The Nigerian leader noted that Clark had continued to command the respect and admiration of Nigerians from different walks of life.
The president urged the nonagenarian to continue to work for the cohesion and progress of the country to the best of his ability for many decades.
“The grand old man marches on, and we pray to God to continue to strengthen him for the good of the country and to serve as a beacon for all those who admire him,” Buhari added.