Kuznets curve. The Kuznets curve is an empirical observation that posits inequality rises and then falls as GDP per capita increases.
Maybe inequality causes economic growth: As income inequality rises, the rich get richer and save more (because richer people have a higher marginal propensity to save than poorer people) so banks have more funds to loan out, investment rises, AD rises, LRAS increases in the long-run so real GDP increases. Although, the rich may not save more, they may import more luxury goods causing imports to rise and AD to fall and also no increase in funds available for investment. The government must ensure the rich increase their savings as they get richer.