: This paper by Jaakko Hämeen-Anttila (2017) is a primary academic source that discusses Nawāḍir al-Ayk and its companion work, al-Wishāḥ
Original idea (from Al-Asma‘i): A Bedouin was asked, “Why don’t you eat onions?” He replied, “Because after its sweetness, it becomes bitter — and after its bitterness, there’s bad breath.” nawadir alayk english pdf better
Let’s address the elephant in the room. You want a free PDF. However, "better" implies curation. Here are the three best sources to get a superior version, ranging from free to premium. : This paper by Jaakko Hämeen-Anttila (2017) is