1 Samuel 19

As Saul sent messengers to find and take David, it just happend as they went forth they came upon Samuel and some of his brethren.  And as they did -

"...when they saw the company of the prophets prophesying, and Samuel standing as appointed over them, the Spirit of God was upon the messengers of Saul, and they also prophesied."  (Old Testament | 1 Samuel 19:20)

Some might wonder what happened to these messengers that they "prophesied".  John the Revelator explained -

"...I am thy fellowservant, and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy."  (New Testament | Revelation 19:10)

This would explain that upon feeling the Spirit of God, they received a testimony of Jesus Christ and bore testimony of such which is the spirit of prophecy.  What is interesting is that -

"...when it was told Saul, he sent other messengers, and they prophesied likewise. And Saul sent messengers again the third time, and they prophesied also."  (Old Testament | 1 Samuel 19:21)

Samuel must have been a powerful teacher for all these to be converted.  Even as the frustrated Saul took it upon himself to pursue David, he asked -

"...Where are Samuel and David? And one said, Behold, they be at Naioth in Ramah.
23 And he went thither to Naioth in Ramah: and the Spirit of God was upon him also, and he went on, and prophesied, until he came to Naioth in Ramah.
24 And he stripped off his clothes also, and prophesied before Samuel in like manner."  (Old Testament | 1 Samuel 19:22 - 24)

Even Saul felt the Spirit of the Lord on this occasion.