Book of Judith, Chapter 13, 9–10: "After which, she went out and gave the head of Holofernes to her maid, who put it in her food bag", and after their return, 15: "She pulled the head out of the bag and held it for them to see.", online
See the discussion on the early copy in the Royal Collection: Royal Collection, "After Titian (c. 1488-Venice 1576), Tarquin and Lucretia, c. 1514–15, Oil on panel, RCIN 402681