Reference : Hisn al-Muslim 150

أللّهُـمَّ اغْفِـرْ لي وَارْحَمْـني 
وَأَلْحِقْـني بِالرَّفـيقِ الأّعْلـى
Allāhumma’ghfir lī warḥamnī 
wa alḥiqnī bir-rafīqi ‘l-'A`alā.

O Allah, forgive me and have mercy upon me, 
and join me with the highest companions (in Paradise).

Reference:
Al-Bukhari7/10, Muslim 4/1893.

Chapter: When the sick have renounced all hope of life