Dressing the baby in elegant clothing:[1]

In honor of the circumcision, the baby, who is the Chasan of the Bris, is to be dressed in elegant clothing similar to the day that he enters the chuppah.

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[1] See Mateh Moshe Seder Mila; Machzor Vitri 505; Even Ezra Shemos 4:5; Kelalei Hmaila p. 64; Koreis Habris 265:60; Bris Avos 7:2; Likkutei Sichos 22:58; Shevach Habris 18:1