There are many translations of the anonymous Sir Gawain and the Green Knight. Depending upon what translation is used, the line numbers for the quote in question will vary. That said, many of the texts I have come across do not have line numbers. The form of the prose is completed, normally, using numbered sections with each section ending with a bob-and-wheel. Therefore, the reference below to the lines numbers for the quote was obtained only through counting the lines until the section in question was found.
In regards to one modern translation, compiled and completed by W. A. Neilson, the lines sought are found in section 12 of "Fytte the First."
You may be sure by this branch that I bear here that I pass by in peace and no plight seek. For were I found here, fierce, and in fighting wise, I had a hauberk at home and a helm both, a shield and a sharp spear, shining bright, and other weapons to wield, I well will, too; but as I wish no war, I wear the softer.
Another translation displays Sir Gawain and the Green Knight in prose form. This is the 2007 translation by A. S. Kline. In Kline's translation, the preceding quote is found in lines 265 through 271, again in section 12.
At the end of the section 12, in the bob-and-wheel ("lines" 275-278), Arthur challenges the Green Knight's intent:
Arthur answered there, and said: ‘Sir courteous knight, if you crave battle bare,here fails you not the fight.’
Athur's men, from the time the Green Knight enters the castle, until Sir Gawain stands to ask permission to take the knight's challenge, remain quiet. Arthur is the only one, prior to Gawain, which challenges the Green Knight.