Tafsir of Sad 38:88

ولتعلمن نبٲه

And you shall certainly know the truth of it, means, `you will see confirmation that what he says is true.'

بعد حين

after a while. (means, soon). Qatadah said, "After death." Ikrimah said, "It means, on the Day of Resurrection.'' There is no contradiction between the two views, because whoever dies comes under the rulings of the Day of Resurrection. This is the end of the Tafsir of Surah Saad. All praise and gratitude is due to Allah, and Allah may He be glorified and exalted, knows best