The Quran

وَدَخَلَ مَعَهُ السِّجنَ فَتَيانِ ۖ قالَ أَحَدُهُما إِنّي أَراني أَعصِرُ خَمرًا ۖ وَقالَ الآخَرُ إِنّي أَراني أَحمِلُ فَوقَ رَأسي خُبزًا تَأكُلُ الطَّيرُ مِنهُ ۖ نَبِّئنا بِتَأويلِهِ ۖ إِنّا نَراكَ مِنَ المُحسِنينَ

Muhammad Asad

NOW two young men happened to go to prison at the same time as Joseph.¹ One of them said: "Behold, I saw myself [in a dream] pressing wine." And the other said: "Behold, I saw myself [in a dream] carrying bread on my head, and birds were eating thereof." [And both entreated Joseph:] "Let us know the real meaning of this! Verily, we see that thou art one of those who know well [how to interpret dreams]."²

Lit., "entered the prison with him". According to the Biblical account (not contradicted by the Qur'an), they were the King's cup-bearer and baker, both of them imprisoned for unspecified offences.
This is the meaning given by Baghawi, Zamakhshari and Baydawi to the expression al-muhsinin in the above context, adopting the tropical use of the verb ahsana in the sense of "he knew [something]" or "he knew [it] well". Thus, the Qur'an indicates here in its elliptic manner that Joseph's reputation for wisdom and dream-interpretation preceded him to prison.