1 Chr 12:20

וּמִֽמְּנַשֶּׁ֞ה נָפְל֣וּ עַל־דָּוִ֗יד בְּבֹא֨וֹ עִם־פְּלִשְׁתִּ֧ים עַל־שָׁא֛וּל לַמִּלְחָמָ֖ה וְלֹ֣א עֲזָרֻ֑ם כִּ֣י בְעֵצָ֗ה שִׁלְּחֻ֜הוּ סַרְנֵ֤י פְלִשְׁתִּים֙ לֵאמֹ֔ר בְּרָאשֵׁ֕ינוּ יִפּ֖וֹל אֶל־אֲדֹנָ֥יו שָׁאֽוּל׃

Some from Manasseh defected to David when he went with the Philistines to fight against Saul. (They did not help the Philistines because the Philistine rulers consulted and sent David away, saying, “It will cost us our heads if he defects to his master Saul.”)