Does the Prophet's sifting of old dates to remove weevils indicate obligation? And is this sifting due to the impurity of the weevils or the prohibition of eating them?

It is stated in 'Awn al-Ma'bud that eating food suspected of containing worms is disliked (makruh), but the food does not become impure (najis) by the presence of worms in it, nor is it forbidden to eat.