He told worshippers at the State House Mosque in Abuja that he was aware of the weight of the responsibilities he owed Nigerians.
Buhari repeatedly expressed gratitude to Nigerians for supporting him to win the February 23 presidential poll.
A State House statement said the President spoke after attending Tafsir, the daily Quranic interpretations marking the Ramadan fast.
“The expectations of Nigerians will be met. I will not let them down.
“I will continue to do my best”, he was quoted as saying in the statement signed by his Senior Special Assistant on Media and Publicity, Garba Shehu.
It added, “President Buhari said the reality of his office weighs heavily on his mind at all times, and he will keep working to deliver an improved life to Nigerians.
“The President said he knows what to do, and will not fail Nigerians.
“President Buhari expressed gratitude to all Nigerians for the opportunity to serve a second term in office.
“He said their expectations for giving him the mandate will be met.”