All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
Asbaab An-Nuzool (Reasons of Revelation), written by the Shaafiʻi scholar Abu Al-Hasan ʻAli ibn Ahmad ibn Muhammad ibn ʻAli Al-Waahidi An-Naysaaboori (d. 468 AH), is one of the useful books in this field without a doubt; however, there are some remarks about it, such as its mention of some very weak ahaadeeth. A number of scholars revised the book; perhaps one of the best revisions is that by Dr. Maahir Al-Fahl. So if you wish to benefit from this book, you should obtain the revised version in order to identify the authentic and weak ahaadeeth therein.
For more benefit, please refer to fatwa 194995.
Allah knows best.