Did the laws of Yahweh exist in the days of Avraham (Abraham)?

Answer From The Annual Reading Schedule - Week 6 Notes For Genesis: Yes (Genesis 26:5). Although commands like the prohibitions of marrying one's sister, tithing to the Lewites (Levites) and Sons of Aharon (Aaron), the Aharonic (Aaronic) priesthood, and Lewites were not yet in place, it is clear there were commands. Such commands most likely included the Sabbath, distinguishing between clean and unclean animals, not killing, stealing, committing adultery, coveting, or committing sexual sins, along with others that Avraham (Abraham) was probably taught from his father as passed down throughout the generations from Adam. We can see the Sabbath given in the Garden of Eden (Genesis 2:3), Noach (Noah) distinguishing between clean and unclean animals (Genesis 8:20), and Sedom (Sodom) and Amorah (Gomorrah) judged for sexual sins (Genesis 19:24). You can click here to read a little about tithing if you want to hear our perspective on this.