Galatians 4:22

4:22 For it is written that Abraham had two sons, one by the ¹  slave woman and the other by the free woman.

[4:22]  ¹ tn Paul’s use of the Greek article here and before the phrase “free woman” presumes that both these characters are well known to the recipients of his letter. This verse is given as an example of the category called “well-known (‘celebrity’ or ‘familiar’) article” by ExSyn 225.