The Ramban wrote a letter to unnamed French rabbis in defense of the Rambam whose books were being banned at that time. "French rabbis" is how he generally refers to the authors of Tosafot (e.g. beginning of Pesachim).
The letter is numbered 2 in the first volume of Kitvey Haramban (published by Mosad Harav Kook). The letter is also available online here but the source isn't indicated.
This is the line where he first addresses the recipients of the letter:
רבותינו הצרפתים, תלמידיכם אנו ומימיכם אנו שותים