《北史·列传·卷七十五》
适逢永昌王仁随太武南征，得到元后姐妹二人，洪之偷偷送去食物，结拜为兄弟，于是就跟亲人一样。
会永昌王仁随太武南征，得元后姊妹二人，洪之潜相饷遗，结为兄弟，遂便如亲。
It happened that King Ren of Yongchang followed Taiwu south to conquer, and got the younger sisters of the empress dowager. Hongzhi secretly sent them food and became sworn brothers, so they became like family.