Here's the rule from the ATP Rulebook.
3) Should a doubles match in an ATP World Tour event be uncontested or fail to be completed, the losing team shall only receive points and prize money from the previous round unless one of the following is applicable:
a) Neither player was in the singles main draw:
b) The withdrawing player is still in the singles competition and at the time of the medical examination is declared unfit to play in the singles of that event or, if no longer involved in the singles competition of that event, is forced to withdraw from the singles of the next tournament in which he is entered.
c) The retiring/withdrawing player had retired/withdrawn from his singles match, which was scheduled the same day; or, if the doubles match is scheduled for a following day the player is examined by the tournament doctor and is declared unfit to play.