Tafsir of As-Saffat 37:37

This is a refutation of them and a denial of their claims by clarifying that what he (peace and blessings be upon him) brought—namely, monotheism—is the established truth upon which evidence has been established and upon which all the messengers have reached a consensus. Where, then, does poetry or madness lie in relation to his (may the Exalted High bless him and grant him peace) lofty standing?

Abdullah [Ibn Mas'ud] read it as "wa sadaqa al-mursalun" (and the messengers confirmed [him]), with the letter dal un-voweled and the word al-mursalun in the nominative case (raf'). This means: and the messengers confirmed him in the glad tidings of his coming and in the fact that he is the last of them.