Lily pollen from stamens of lilies can be a real problem and cause disastrous results.
Most importantly DO NOT PUT WATER ON IT. Instead, smother the pollen with talcum/baby powder, leave for a few days and vacuum off. The pollen should absorb into the powder. If the staining is still present call us.
To avoid the chance of staining your carpet in the first place, cut out the stamens altogether from the lily.
Enjoy your lilies!