مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4304
Musnad of Abdullah bin Mas'ood
Abdullah said: The Messenger of Allah (ﷺ) said: “Allah does not send down any disease but He also sends down a remedy with it." On one occasion ‘Uthman said: "... but He sends down a remedy for it; those who know it know it and those who do not know it do not know it."
Musnad Ahmad 4334Saheeh because of corroborating evidence]