While receiving his certificate of return in Abuja on Wednesday, Buhari said the elections have been adjudged to be free and fair by local and foreign observers.
He said, "From the comments of observers, both local and foreign, it is obvious that the elections were both free and fair.
"Now that the elections are over and the winner declared, we must all see it as a victory for Nigeria, our dear country.
"That's why I encouraged my team of supporters, in a speech I read earlier today, not to gloat. Our God-given victory is enough cause for joy without deriding those who are in the opposition."
The president congratulated all the candidates who participated in the election on a hard-fought campaign and appealed for unity in the best interest of Nigeria.
"Our government will remain inclusive and our doors will remain open. That is the way to build the country of our dreams - safe, secure, prosperous and free of impunity and primitive accumulation by those entursted with public office," he said.
Even though he adjudged the Presidential and National Assembly elections conducted on Saturday, February 23 to have been conducted in "an overwhelmingly peaceful manner", he sympathised with families of those killed through accidents and "mindless violence".
"Election is not war. I pray that we all accept this democratic approach to elections, however contentious," he concluded.
Atiku kicks against Buhari's victory
In a signed statement released on Wednesday, Atiku refused to accept the result, alleging that the election was plagued by electoral malpractices that disenfranchised millions of people who voted for him or were willing to.
He alleged that there was widespread voter suppression in his stronghold states across the country while there were questionable voter turnout rates in the president's strongholds.
He also condemned the militarisation of the process which he said was a return to the era of military dictatorship that should not be allowed to stand.
He assured his supporters that he'll not allow Nigeria's democracy to be debased unchallenged and vowed to challenge the result of the 2019 presidential election in court.