The person spoke on condition of anonymity Sunday night because the team had not yet made an announcement, which was expected in the next few days.
Pettitte's son, Josh, posted the news on Twitter earlier Sunday and said Andy Pettitte day at Yankee Stadium will be Aug. 23, when New York plays the Cleveland Indians.
Pettitte helped the Yankees win five World Series championships. He ranks third in team history with 219 wins and first in strikeouts with 2,020. The left-hander retired in 2013 after spending 15 of his 18 major league seasons in pinstripes.
A three-time All-Star, Pettitte was MVP of the 2001 AL Championship Series and owns big league post-season records for wins (19) and starts (44).