They told him that they had left him by their belongings while they went out to race, and the wolf came and ate him. They smudged his undershirt with fake blood and showed it to their father. In fact they had thrown Yusuf pbuh into the well.
(They cried, “Our father! We went racing and left Yusuf pbuh with our belongings, and a wolf devoured him! But you will not believe us, no matter how truthful we are.” And they brought his shirt, stained with false blood.) Yusuf 12:17
قالوا لأبيهم أنهم ذهبوا ليتسابقوا و تركوا ثيابهم و أشياءهم فتركوا يوسف عند الأغراض . فجاء الذئب و أكله. و قد أحضروا قميصه و عليه دم كاذب. و هم بالواقع أنزلوه إلى البئر كما أشار عليهم أحد الإخوة.
(قَالُواْ يَٰأَبَانَآ إِنَّا ذَهَبْنَا نَسْتَبِقُ وَتَرَكْنَا يُوسُفَ عِندَ مَتَاعِنَا فَأَكَلَهُ ٱلذِّئْبُ وَمَآ أَنتَ بِمُؤْمِنٍ لَّنَا وَلَوْ كُنَّا صَادِقِينَ. وَجَاءُوا عَلَىٰ قَمِيصِهِ بِدَمٍ كَذِبٍ ۚ)
يوسف 12: 17