The Interpretation of the Dreams
When Yusuf finished calling them, he started interpreting their dreams for them, Yusuf said,
يَا صَاحِبَيِ السِّجْنِ أَمَّا أَحَدُكُمَا فَيَسْقِي رَبَّهُ خَمْرًا
O two companions of the prison! As for one of you, he will pour out wine for his master to drink;
to the man who saw in a dream that he was pressing wine. He did not direct this speech at him, however, so that to lessen the grief of the other person.
This is why he made his statement indirect,
وَأَمَّا الاخَرُ فَيُصْلَبُ فَتَأْكُلُ الطَّيْرُ مِن رَّأْسِهِ
and as for the other, he will be crucified and birds will eat from his head.
which is the interpretation of the other man's dream in which he saw himself carrying bread above his head.
Yusuf told them that the decision about their matter has already been taken and it shall come to pass. This is because the dream is tied to a bird's leg, as long as it is not truthfully interpreted. If it is interpreted, then it becomes a reality.
Ath-Thawri said that Imarah bin Al-Qa`qa` narrated that Ibrahim said that Abdullah bin Mas`ud said,
"When they said what they said to him, and he explained their dreams to them, they replied, `We did not see anything at all.' This is when he said,
قُضِيَ الَامْرُ الَّذِي فِيهِ تَسْتَفْتِيَانِ
Thus is the case judged concerning which you both did inquire."
The understanding in this is that he who claims that he saw a dream and was given its interpretation, then he will be tied to its interpretation, and Allah has the best knowledge.
There is an honorable Hadith that Imam Ahmad collected from Mu`awiyah bin Haydah that the Prophet said,
الرُّوْيَا عَلَى رِجْلِ طَايِرٍ مَا لَمْ تُعْبَرْ فَإِذَا عُبِرَتْ وَقَعَت
The dream is tied to a bird's leg, as long as it is not interpreted. If it is interpreted, it becomes a reality