Allāh said:

يَا بُنَيَّ لَا تَقْصُصْ رُؤْيَاكَ عَلَىٰ إِخْوَتِكَ فَيَكِيدُوا لَكَ كَيْدًا ۖ
“O my son, do not relate your vision to your brothers or they will contrive against you a plan.”
[Yūsuf, 12:5]

Imām ʿAbd al-Raḥmān ibn Nāṣir al-Saʿdī (d. 1376 AH) comments: 

From [among the benefits of the story of Prophet Yūsuf (عليه السلام)] is that it is from the prudence of a slave [of Allāh] that—should he choose to engage in an action—he must thoroughly examine it from all angles, such that he has taken into account all possibilities. 

The cautiousness exhibited here [manifests itself] as a form of non-harmful negative thinking, so long as what he surmises is left unfulfilled. Rather, he should be cautious about the occurrence of any harmful outcome, even if this involves assuming the worst of another. [This is permissible] if there exist indications that justify or stipulate [negative assumptions]. This is the case in this verse and similarly in his perception of strong indications in His saying: 

قَالَ هَلْ آمَنُكُمْ عَلَيْهِ إِلَّا كَمَا أَمِنتُكُمْ عَلَىٰ أَخِيهِ مِن قَبْلُ
“He said, “Should I entrust you with him except [under coercion] as I entrusted you with his brother before?”
[Yūsuf, 12:64]

For they [the sons of Yaʿqūb] had already done to his brother [Yūsuf] what they did [of harm]. Thus, there is no blame on Yaʿqūb for holding such an assumption in regards to them. Even if they had never behaved carelessly nor attempted to harm their youngest brother [Binyamīn]. 

Source: Fawāʾid Qiṣṣah Yūsuf: 22
Translated by: Riyāḍ al-Kanadī