No beats Um Koultoum (one of many possible spellings of her name), who had been known to stretch two or three songs out for as long as 6 hours in performance, and whose popular recordings could run to an hour-
From her Wikipedia entry:

The duration of Umm Kulthum's songs in performance was not fixed, but varied based on the level of emotive interaction between the singer and her audience. A typical improvisatory technique of hers was to repeat a single phrase or sentence of a song's lyrics over and over, subtly altering the emotive emphasis and intensity each time to bring her audiences into a euphoric and ecstatic state, and was considered to "have never sang a line the same way twice". Thus, while the official recorded length of a song such as Enta Omri (You Are My Life) is approximately 60 minutes, a live performance could extend to many hours as the singer and her audience fed off each other's emotional energy. This intense, highly personalized creative relationship, was undoubtedly one of the reasons for Umm Kulthum's tremendous success as an artist.

here are some recordings--http://www.oumkalthoum.org/audio/ though I suspect only Jack Campin will listen to them--