Sunnah.com reference : Book 7, Hadith 52English translation : Book 7, Hadith 825Arabic reference : Book 7, Hadith 822
Narrated Ibn Mas'ud (RA):
Allah's Messenger (ﷺ) said: "Do not buy the fish that is in the water, for it involves uncertainty (risk)."

[Reported by Ahmad who indicated that the correct view is that it is Mawquf (saying of a Companion, i.e. Ibn Mas'ud].
وَعَنِ اِبْنِ مَسْعُودٍ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ لَا تَشْتَرُوا اَلسَّمَكَ فِي اَلْمَاءِ; فَإِنَّهُ غَرَرٌ }  رَوَاهُ أَحْمَدُ, وَأَشَارَ إِلَى أَنَّ اَلصَّوَابَ وَقْفُهُ  1‏ .‏‏1 ‏- ضعيف.‏ رواه أحمد ( 3676 )‏.‏