What are the sayings of the scholars regarding the indication of 'Umar ibn al-Khattab's statement to Anas, "The grave, the grave," as evidence that prayer at graves is not invalidated?

The action of Anas praying at a grave, and Umar seeing him and not ordering him to repeat the prayer, is used as evidence that prayer at graves is not invalidated. Most jurists hold the view that the prayer is valid, though disliked, and that the prohibition against praying towards graves is to be understood as a matter of dislike (makruh). Those who argue for the invalidity of such prayers are refuted by stating that Anas was unaware of the grave's presence and did not intentionally pray towards it.