For those who may be wondering what we are on about, the Book of Jasher
is a collection of Jewish legends relating to biblical history, first appearing in 1625. it was published in English in 1840 and became fairly popular among the LDS, even being reprinted in Salt-Lake during the 1880s.
An easily accesible anthology of Jewish legends in English is Louis Ginzberg's Legends of the Jews.
The portion dealing with Abraham is found here
, but I also highly recommend consulting vol. V,