The Messenger of Allah ﷺ used to show us the day before the battle the very spots where the people of Badr would fall. He would say, "This is where so-and-so will fall tomorrow, if Allah wills."He said, "By the One who sent him with the truth, they did not miss the boundaries that the Messenger of Allah ﷺ had marked out." Then they were thrown into a well, one on top of another.
إن رسول الله ﷺ كان يرينا مصارع أهل بدر بالأمس، يقول: هذا مصرع فلان غدا إن شاء الله قال: فوالذي بعثه بالحق ما أخطؤوا الحدود التي حد رسول الله ﷺ، قال: فجعلوا في بئر بعضهم على بعض.
Muslim narrated it in the chapter on Paradise (2873), from Ishaq bin Umar bin Sulayt Hudhali, who said, Sulayman bin Mughira told us, from Thabit, who said, Anas said, "I was with Umar between Makkah and Madinah, and we tried to sight the new moon. I had sharp eyesight, and I saw it, though no one else claimed to have seen it besides me."He said, "I kept saying to Umar, 'Don't you see it?' But he could not see it. Umar said, 'I will see it while lying on my bed.'"Then he began telling us about the people of Badr, and he related it.