Dals should be washed *before* soaking to remove any surface impurities and dust, allowing for cleaner soaking water.
Washing dals before soaking is crucial for several reasons. First, it removes any dirt, debris, or residual pesticides that may be present on the surface of the lentils. This ensures that you're starting with a cleaner product. Second, washing helps to remove excess starch, which can sometimes make the soaking water cloudy and potentially affect the cooking process. By washing beforehand, you're essentially preparing the dals for optimal soaking and subsequent cooking. The soaking process itself helps to soften the dals, reducing cooking time and improving digestibility. Washing after soaking would mean that the dals have already absorbed the impurities from the soaking water, which is not ideal.
After washing the dals, check for any small stones or debris that may have been missed during processing. It's easier to spot these when the dals are wet and spread out in a bowl.