Mishkat al-Masabih 4537
Asma’ daughter of ‘Umais told that the Prophet asked her what laxative she used and she replied that she used spurge, whereupon he declared that it was very hot. She then used senna as a purgative, and. the Prophet said:
“If anything contained a remedy for death it would be senna.” 

Tirmidhi and Ibn Majah transmitted it, Tirmidhi saying this is a hasan gharlb tradition.
وَعَن أَسْمَاءَ بِنْتِ عُمَيْسٍ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ سَأَلَهَا: «بمَ تستَمشِينَ؟» قَالَت: بالشُّبْرمِ قَالَ: «حارٌّ حارٌّ» . قَالَتْ: ثُمَّ اسْتَمْشَيْتُ بِالسَّنَا فَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَوْ أَنَّ شَيْئًا كَانَ فِيهِ الشِّفَاءُ مِنَ الْمَوْتِ لَكَانَ فِي السَّنَا» . رَوَاهُ التِّرْمِذِيُّ وَابْنُ مَاجَهْ وَقَالَ التِّرْمِذِيُّ: هَذَا حَدِيث حسن غَرِيب