Must a traveller repeat a combined and shortened prayer already performed after leaving his town if he turns back home to fetch a forgotten item?

Summary

A combined and shortened prayer performed after passing the boundary of one's residence, with the intention of travelling beyond two marhalah, is valid. If the person then returns home for a need, the prayer already performed is not invalidated and need not be repeated. However, once he intends to return or begins returning to his hometown, he is considered a resident and may not shorten or combine prayers until he again leaves the boundary of his town.

Written in our own words from the original fatwa — check the source before acting on it.