The easiest way will depend on a few factors. If this is this a glass type basin, try filling the basin with warm water. This will help loosen the glue. I wouldn't add boiling water to any type of basin. If the label is on the outside, and the basin is installed, a warm damp cloth will also help to remove the paper label.
The remaining glue can be removed with an oil-based product such as baby oil, or mayonnaise. Check that there will be no color change by experimenting with a small amount in a hidden area.