Whitney Houston's Sister-In-Law Pat Houston -- No Foul Play

Whitney Houston's sister-in-law has backed off her insinuation that Whitney Houston died as a result of foul play.

Pat Houston was at LaGuardia Airport early this AM when our photog asked her if she believed foul play was involved, and she said no.

You'll recall ... Pat told Oprah she did not know how Whitney ended up in the tub, suggesting her death was something other than an accident. It's unclear if Pat knew that Whitney's body was found face down in the tub and if that's why she had doubts at the time.