For some reason I feel like I have heard somewhere that Lincoln was Jewish. My friend said I was wrong, so we bet alcohol over who is right. So was Abraham Lincoln Jewish or not (aka who is buying the next round of booze)?
No, Abraham Lincoln was never Jewish nor of Jewish descent.
Someone was probably thrown by the name Abraham, because they believe only Jews use the name, or most Old Testament names that weren't Christianized by being used by saints (St. John, St. Elizabeth and so on). However, they were occasionally used by early medieval Franks, by Early Modern English Puritans when not using what Camden called "the new names", and by any Bible-reading Protestants in the 18th & 19th C.
For example, in 1880, the earliest year SocSec provides, Abraham was the 163rd most popular name for boys born. This was topped by Old Testament names like Samuel at #17, & Isaac at 62.