Which work by Archimedes preserves a report of Aristarchus's Sun-centered hypothesis?

The work by Archimedes that preserves a report of Aristarchus’s Sun-centered hypothesis is The Sand Reckoner.

Written in the 3rd century BCE and also known by its Greek title Psammites, the treatise investigates how many grains of sand might fill the universe. To make that calculation possible, Archimedes used a very large universe modeled on Aristarchus’s proposal: Earth rotates and travels around a stationary Sun, while the fixed stars lie at an immense distance.

Aristarchus’s own work on heliocentrism has not survived, so Archimedes’s account is one of the most important surviving witnesses to it. The description is brief, but it explains why a Sun-centered system required an enormous stellar sphere: observers had not detected stellar parallax, so the stars had to be extremely far away.

A common mix-up is to choose Measurement of a Circle because it is another astronomical work by Archimedes. That treatise concerns geometry and the value of pi; The Sand Reckoner is the work that preserves the famous ancient report of Aristarchus’s cosmology.