There is a Muhammad saying about a giant tree,
“In Paradise there is a tree in whose shade a rider could travel for a hundred years without crossing it.”
According to this World Building StackExchange conversation, a horse rider can realistically travel about 50 km a day. This means the shade being mentioned is more than 1,825,000 km long, or a radius of 3,650,000 km assuming a circular overall shade shape.
There is a unit of distance mostly used to measure the size of stars called Solar radius. As the name says, it is based on the radius of our sun, so 1 Solar radius equals to about 695,700 kilometres.