In Baldur's Gate, this weapon can be obtained after the party talks with the Merry Fools in the Helm and Cloak Inn, a group called the Undermountain walks in, and if the party is rough to them, they will start fighting. One of the warriors in that group drops the axe when killed.
The battle axe +2 which looks like this one can be obtained in Baldur's Gate II in the Planar Sphere, in the room with the Lizard Men, in a "wall" container.
|“||Battle axe +2: 'Battle Axe of Mauletar.' During the Tethyr civil war, the Battle Axe of Mauletar was in the possession of the house of Ormynd. This family was betrayed while trying to flee the country, and Mauletar, lead guard and personal friend, took up the axe and sacrifiiced himself to buy enough time for his companions to flee. His battle cry was favored by the gods, and was echoed across the lands as a symbol of devoted friendship and loyalty. Thus, the magical axe was used to uphold these virtues, to be used against those who lacked honor and courage.||”|