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.
أَنَّ النَّبِيَّ ﷺ نَهَى عَنْ هَاتَيْنِ الشَّجَرَتَيْنِ وَقَالَ مَنْ أَكَلَهُمَا فَلاَ يَقْرَبَنَّ مَسْجِدَنَا وَقَالَ إِنْ كُنْتُمْ لاَ بُدَّ آكِلِيهِمَا فَأَمِيتُوهُمَا طَبْخًا قَالَ يَعْنِي الْبَصَلَ وَالثُّومَ