Midrasch zu Bamidbar 22:8

8 (Numb. 22:7) “So the elders of Moab and the elders of Midian went with [the tools for] divination in their hand,” for they brought in their hands all kinds of divining instruments through which one divines, so as not to give him an excuse [for not coming]. So the divining instruments were in the hands of the elders of Midian, for they said, “If he comes with us, he will succeed; but if he delays [even] for an hour, he will be of no use.” As soon as they saw that he said (in vs. 8), “Lodge here tonight,” the elders of Midian went away, because they knew through their divinations that he would be of no use.