Tafsir of An-Nahl 16:122

(And We gave him in the world a good thing): [This means] that He caused people to love him, to the extent that all followers of religions hold him in high regard and praise him, just as he had requested by saying: (And grant me a tongue of truth among the later ones). This has been narrated from Qatadah and others.

According to Al-Hasan, the "good thing" is prophethood. It has also been said that it refers to righteous children in his old age, or wealth which he spent in ways of goodness and righteousness, or a long life spent in prosperity and obedience. Under the first interpretation, "a good thing" means a good biography, while in the subsequent interpretations, it refers to a good gift or blessing. Thus it has been said, and it is permissible in all cases to mean a good gift. The shift to the first-person plural [in "We gave him"] is to demonstrate the perfection of care for his affairs and to magnify his status, peace be upon him.

(And indeed, in the Hereafter, he will be among the righteous): He is included in their number, existing with them in the high ranks of Paradise, just as he had requested by saying: (And join me with the righteous). By "the righteous," he meant the prophets, peace be upon them.