Laid To Rest (Side Quest)
The side quest becomes available immediately on finishing the Fish out of Water side quest.
Travel to Aaru, the afterlife accessible via Nefertiti's tomb, and speak to the merchant in the House of Threshed Grain to complete the quest. Note that, in addition to a healthy XP reward, you also get an ability point.
Which is karmicly generous, but raises a lot of questions. How is the merchant here already- has he even been buried yet? Do all merchants go to Nefertiti's boutique heretical afterlife? Because there's not a lot of people here. Also, all this time Bayek has been carting loot out of the actual land-beyond-death, I can't imagine there's not a market for that. Plus, where are the merchant's grave goods? And if he did have them, and then Bayek brought him the 'real ones' from his tomb, would he have two of each? If they were stolen in one place, would they disappear from the other? A lot of metafiddickal mystery here that never gets unpacked….