“Now Abraham took another wife, whose name was Keturah.” Gen. 25:1
Although most see no real issue with Abraham taking a wife at this point (Sarah having passed away, and Hagar having been sent away with God’s approval quite some time ago), many Jewish scholars (including Rashi) believe that Keturah is actually Hagar.
Keturah’s name is similar to the Hebrew word qetoret, which means incense (or to burn incense) or possibly sacrifice . This alludes to beautiful deeds, or answered prayer. The belief is that Hagar, after having been sent away from Abraham dabbled in idolatry but repenting of it, and ultimately stayed chaste and otherwise became righteous. Some also believe that Keturah’s name was derived from an incense trade route.
We have virtually no background information on Keturah, so nothing in the scriptures specifically contradicts the idea that Keturah and Hagar could be one and the same; the only obvious difference is in name – but a name change, either by God, in a legal sense or even as a term of endearment – is not an impossibility, as we see many other such examples in the scriptures.
For those who have not heard this theory before, it is generally not understood why such a theory would even exist, or perhaps wishful thinking; however it would make sense that the hope that Father Abraham could always, through the lens of history, be looked at as one of the most righteous men of faith, there is cause not to want to view him as an adulterer. After all, Hagar technically did become Abraham’s second wife (Gen. 16:3) so as long as she is alive, Abraham cannot re-marry according to the law, even though it may be acceptable in the local culture.
It is worth noting that in 25:6 a reference is made to the “sons of [Abraham’s] concubines”; however many agree this is a mistranslation, and that the term is technically singular (i.e. concubine) and would better have been rendered ‘concubinage’ or similar.