"And send him with me as a reinforcement [rid'an]," meaning: an aid. "Verily he will confirm me [yusaddiquni]," meaning: he will be with me in the Message. "Indeed, I fear that they will deny me."
Muhammad said: It is said, "rada'tuhu 'ala kadha," meaning: I aided him. He who reads "yusaddiqni" (with the jussive) does so as the response to the request: "Send him, [so that] he may confirm me." He who reads "yusaddiquni" (with the nominative) the meaning is: as a reinforcement confirming me.
Ibn Mujahid mentioned that Nafi' alone read it as "riddan," with nunation and without a glottal stop [hamzah], while the rest of the reciters read it as "rid'an," with the glottal stop.
Surat al-Qasas from (verse 36 to verse 38).