Who allied with Austria and declared war on Russia.?

Prussia allied with Austria during the Seven Weeks' War in 1866 and declared war on Russia in 1866. However, it's important to clarify that Austria and Prussia were adversaries in that conflict; it was the Franco-Prussian War of 1870-1871 that had Prussia allied with other German states against France, not Russia. The context may vary depending on the historical period in question, so specifying the exact conflict is crucial.