Hadithcore
Mishkat al-Masabih, 3356, 3357

Umm Salama told that the Prophet (ﷺ) was saying during his illness, “Maintain the prayer and care for your slaves.” Baihaqi transmitted it in <i>Shu'ab al-iman</i>, and Ahmad and Abu Dawud transmitted something similar on the authority of ‘Ali.

وَعَنْ أُمِّ سَلَمَةَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ كَانَ يَقُولُ فِي مَرَضِهِ: «الصَّلَاةَ وَمَا مَلَكَتْ أَيْمَانُكُمْ» . رَوَاهُ الْبَيْهَقِيُّ فِي شعب الْإِيمَان وَرَوَى أَحْمَدُ وَأَبُو دَاوُدَ عَنْ عَلِيٍّ نَحْوَهُ

References1 variant
In-Book Reference
Book 13, Hadith 270