It took place in November of 1979.
Not to take the discussion further off topic, but I don’t see how the Shias can be blamed for the massacre in 1987. The Iranian hujjaj were staging a largely peaceful (though admittedly pro-Khomeini) demonstration along a preplanned route as they had for years, with full knowledge of the Saudi authorities. The Saudi government tried to suppress the demonstration, and ultimately resorted to opening fire on unarmed hujjaj, with anywhere from 400-1,500 people shot, beaten, or trampled to death (most of them women and crippled veterans of the Iran-Iraq War). It was at best, a galling example of Saudi police brutaliy, and at worst, a shameless massacre of Shia pilgrims just outside the gates of the house of God. Either way, I don’t see how this would be used “against Shias.”