Numbers 25:6

while they were weeping The reason for their weeping is not found till Numbers 25:8 f.; a plague had been sent. The beginning of the narrative stating the reason for the plague has been lost. But it was probably a punishment for the general immorality of which Numbers 25:6 relates one instance.

It has been conjectured that the lost portion of the story related that Balaam persuaded the Midianites to seduce the Israelites into intermarriage with them in order to provoke Jehovah's anger. In this case Balaam lived (according to P) not in Mesopotamia or Ammon (see on Numbers 22:5) but in Midian. The conjecture receives support from Numbers 31:8; Numbers 31:16.