قُلْ إِنِّى نُهِيتُ أَنْ أَعْبُدَ ٱلَّذِينَ تَدْعُونَ مِن دُونِ ٱللَّهِ لَمَّا جَآءَنِىَ ٱلْبَيِّنَٰتُ مِن رَّبِّى
"Say: 'When the clear proofs came to me from my Lord, I was forbidden to serve those you call upon besides God.'"
The sentence's note of time must be recorded: lammā jāʾaniya'l-bayyināt — "when the clear proofs came".
That is, the refusal is described not as a rejection from the outset but as a position taken after the proof had come.
This coincides exactly with the measure of the sūra: in the thirty-fifth verse those who dispute were characterised as bi-ghayri sulṭānin (with nothing to stand on). Here the side that is speaking states its own ground.
نُهِيتُ — passive: "I was forbidden". The verb does not belong to him. The same line as that treated at al-Aḥqāf 46/9 (in attabiʿu illā mā yūḥā ilayy): the source is not in himself.