It wasnarrated from Abu Sa'eed Al-Khudri that the Messenger of Allah(ﷺ) said:
"When you enter upon one who is sick, cheer him up andgive him hope of a long life, for that does not change anything (ofthe Divine Decree), but it will cheer the heart of the one who issick." (ES)
English reference (ES): Vol. 1, Book 6, Hadith 1438 (ES)
Arabic reference (ES): Book 6, Hadith 1505 (ES)