The Messenger of Allah ﷺ forbade the foul remedy, meaning poison.
حدثنا أبو بكر بن أبي شيبة حدثنا وكيع عن يونس بن أبي إسحق عن مجاهد
نهى رسول الله ﷺ عن الدواء الخبيث يعني السم
[Its isnad is sahih] Abu Dawud narrated it in the Book of Medicine, chapter on disliked medications, no. 3870, from the hadith of Yunus with this same wording. Tirmidhi also narrated it, no. 2045, and Hakim graded it sahih according to the criteria of the two sheikhs, 4/410, and Dhahabi agreed with him.