Where do you find the scripture pertaining to stirring up strife among the brethren?

Answer:
We should strive to dwell together in unity.

Psalms 133:1 [A Song of degrees of David.] Behold, how good and how pleasant it is for brethren to dwell together in unity!

And God hates when someone (in the body of Believers) causes division:

Proverbs 6:16-19 These six things doth the LORD hate: yea, seven are an abomination unto him: A proud look, a lying tongue, and hands that shed innocent blood, An heart that deviseth wicked imaginations, feet that be swift in running to mischief, A false witness that speaketh lies, and he that soweth discord among brethren.

1 Corinthians 12:25 That there should be no schism in the body; but that the members should have the same care one for another.