Does every ablution (wudu') purify sins, or is that limited only to ablution for obligatory or supererogatory prayers?

Ablution (wudu') is a great act of worship, and there is indeed evidence encouraging its performance. Among these is what Imam Muslim narrated from Abu Hurairah that the Messenger of Allah, peace and blessings be upon him, said: "When a Muslim or a believing servant performs ablution and washes his face, every sin he committed with his eyes will be washed away from his face with the water, or with the last drop of water. When he washes his hands, every sin he committed with his hands will be washed away from his hands with the water, or with the last drop of water. When he washes his feet, every sin he committed with his feet will be washed away with the water, or with the last drop of water, until he emerges pure from sins." And ablution here encompasses every legally prescribed ablution, whether for an obligatory prayer, a supererogatory prayer, or other purposes.