The upper legislative chamber also resolved to send a high-powered delegation to commiserate with his family.
By the motion, Buhari officially drew the attention of the senators to the demise of Ajimobi.
The former Oyo governor died in June at the age of 70.
Ajimobi did not recover after he fell into a coma at First Cardiology Consultants Hospital, Ikoyi, Lagos, where he was receiving treatment for COVID-19.
His remains have since been buried according to Islamic rites.
In March, Ajimobi emerged deputy national chairman of the All Progressives Congress (APC) in the south-west but he was not involved in strategic meetings held ahead of the Edo and Ondo elections.
Due to his absence, Hillard Eta, vice chairman (south-south), was asked to stand in for Ajimobi.
However, the APC national working committee (NWC) which he belonged to was coincidentally dissolved on the same day he died.
Also speaking on the floor of the senate, Ibikunle Amosun, senator representing Ogun central, said the late Ajimobi was a man who loved his people.
“He loved his people,” Amosun said while speaking on how he met Ajimobi.
The motion was adopted after it was put to a voice vote by Senate President Ahmad Lawan.