Senate spokesman, Senator Abdulahi Sabi, made the disclosure to reporters Tuesday afternoon.
Sabi explained that there is no time frame for resumption in the letter submitted to National Assembly by Buhari.
He said the letter stated that Mr. President decided to extend his vacation for him to complete and receive the results of a series of tests recommended by his doctors.
"We can now confirm to you that we are in possession of Mr. President's letter to extend his vacation in order to complete and receive the results of a series of test recommended by his doctors", he disclosed.
Buhari had on January 19 written to the National Assembly, notifying the legislature that he was proceeding on a 10-day leave, to return on February 6.
President Buhari also transferred presidential power to the Vice President, Prof. Yemi Osinbajo.