Assalamu'alaikum sister,
I do not know which hadith the Sheikh is referencing to, but here are some hadiths about the medicine:
http://www.searchtruth.com/book_display.php?book=71&translator=1
السلام عليكم ورحمة الله وبركاته
I'm sure many of you heard lots of stories about people with uncurable diseases get cured over night just like that..
Allah created both diseases and cures for them, But as we all know many cures failed to cure some cases when it worked just fine with others of the same diseases.
No matter how powerful a cure is, It never heals without the will of Allah.
And in some cases with Allah's willing will get cured without even a cure.