Jannah is a reward for the one whose best friend passes away
Messenger of Allah ﷺ said, "Allah says, 'I have nothing to give but Paradise as a reward to my believer slave, who, if I cause his dear friend (or relative) to die, remains patient (and hopes for Allah's Reward).
أَنَّ رَسُولَ اللَّهِ ﷺ قَال «يَقُولُ اللَّهُ تَعَالَى: مَا لِعَبْدِي الْمُؤْمِنِ عِنْدِي جَزَاءٌ إِذَا قَبَضْتُ صَفِيَّهُ مِنْ أَهْلِ الدُّنْيَا ثُمَّ احْتَسَبَهُ إِلاَّ الْجَنَّةُ۔»