Chabad.org — English translation + Rashi
Torah Temimah points to Menachos 104b.
E-Daf.com — Menachos 104b
HebrewBooks / Shas PDF
English: It was taught: All may come in partnership.
Ribbuy of joint voluntary minchah — partnership is permitted for a free-will flour offering.
Two or more people may jointly bring a voluntary minchah. Partnership is not available for an obligatory minchah. The language of the verse that opens the voluntary flour-offering section supports the inclusion of partners for a free-will gift of this type.