Khalid said: AbuZiyad Khiyar ibn Salamah asked Aisha about onions. She replied: The last food which the Messenger of Allah ﷺ ate was some which contained onions. (Using translation from Abū Dāʾūd 3829)  

«إِنَّ آخِرَ طَعَامٍ أَكَلَهُ رَسُولُ اللهِ ﷺ طَعَامٌ فِيهِ بَصَلٌ»  

The Messenger of Allah ﷺ forbade these two plants (i.e. garlic and onions), and he said: He who eats them should not come near our mosque. If it is necessary to eat them, make them dead by cooking, that is, onions and garlic. (Using translation from Abū Dāʾūd 3827)   

عَنِ النَّبِيِّ ﷺ قَالَ «مَنْ أَكَلَ مِنْ هَاتَيْنِ الشَّجَرَتَيْنِ الْخَبِيثَتَيْنِ فَلَا يَقْرَبَنَّ مَسْجِدَنَا فَإِنْ كُنْتُمْ لَا بُدَّ آكِلِيهِمَا فَأَمِيتُوهُمَا طَبْخًا»