From Aidan Levy's Rollins bio, pp. 272-3:
Sonny had to find a new rhythm section, fast. He had arranged with Blue Note to record a live album at the Vanguard on November 3, his first live album and the first to be recorded there. He called Donald Bailey - the bassist, not the drummer - who was available. It was likely at the Tijuana in Baltimore, where Bailey was in the house rhythm section, that he met Sonny and Miles. Bailey was a first-call bassist in Baltimore, having performed with Parker, Monk, and Roach. He "played like he's singing," as his children remembered it.
Bailey was a family man, with five children, and life on the road was not conducive to his responsibilities. He worked for the US Postal Service in Baltimore for thirty-three years, but his daughter said, "His real job was music. Every night, he would get home at two o'clock in the morning, and get up at six to be at the post office. He did that every day."