The 1996 collision between the French Cerise military reconnaissance satellite and debris from an Ariane rocket.
The 2009 collision between the Iridium 33 communications satellite and the derelict Russian Kosmos 2251 spacecraft, which resulted in the destruction of both satellites.
The 22 January 2013 collision between debris from Fengyun FY-1C satellite and the Russian BLITS nano-satellite.
The 22 May 2013 collision between two CubeSats, Ecuador's NEE-01 Pegaso and Argentina's CubeBug-1, and the particles of a debris cloud around a Tsyklon-3 upper stage (SCN 15890)[1] left over from the launch of Kosmos 1666.
One of those was a real satellite to satellite collision.
The 2009 collision between the Iridium 33 communications satellite and the derelict Russian Kosmos 2251 spacecraft, which resulted in the destruction of both satellites.
Satellite collision - Wikipedia
Fortunately they are rare. Satellites are getting more. But satellite tracking and collision avoidance is also getting better.
Much worse is space debris by not deorbited dead satellites and upper stages that are not properly passivised and explode later. Notorious are old US spy sats and ULA upper stages. But russian upper stages too. They use many of them. Reason is usually not properly terminated batteries, sometimes residual propellant that should have been vented.