It is narrated from Sayyidah Asma' (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) came to her while she had some shubrum (a strong purgative herb) which she was pounding. The Prophet (peace and blessings be upon him) said: "What are you doing with this?" She said: O Prophet of Allah! I will give it to so-and-so to drink. The Prophet (peace and blessings be upon him) said: "It is a disease." Then he (peace and blessings be upon him) came to her while she had some senna (a medicine), and he (peace and blessings be upon him) said: "What are you doing with this?" She said: So-and-so will drink it. He (peace and blessings be upon him) said: "If anything were able to ward off death, it would be senna."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20732