700 – Ibn Masʿūd (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace be upon him) declared, “Do not buy fish while it is still in the water, for that is gharar (excessive uncertainty).” Aḥmad narrated it and indicated that the correct stance is that it is mawqūf ⦗1⦘.

––
Hadith grading:
The report is mawqūf (halted at the Companion), though a marfūʿ (Prophetic) version is also transmitted. In legal matters the mawqūf wording carries the force of a marfūʿ report; Allah knows best.
Al-Talkhīṣ states: “Aḥmad transmitted it both marfūʿ and mawqūf through Yazīd ibn Abī Ziyād, from al-Musayyab ibn Rāfiʿ, from him.”
Al-Bayhaqī said: “There is a break between al-Musayyab and ʿAbd-Allāh, and the sound position is that it is mawqūf.”
Al-Dāraquṭnī commented: “The mawqūf wording is more authentic,” a judgement shared by al-Khaṭīb and Ibn al-Jawzī.
A marfūʿ report from ʿImrān ibn Ḥuṣayn was narrated by Ibn Abī ʿĀṣim. Al-Haythamī remarked: “Aḥmad narrated it both mawqūf and marfūʿ, and al-Ṭabarānī in al-Kabīr did likewise. The transmitters of the mawqūf chain are those of the sound collections, whereas in the marfūʿ chain appears Aḥmad’s shaykh Muḥammad ibn al-Sammāk, for whom I found no biographical entry; the remaining narrators are trustworthy.” End quote.
This narration also comes under the general prohibition of trading that involves gharar.

What is derived from the two hadiths:
1 – Ṣaḥīḥ Muslim records, in the narration of Abū Hurayrah, that “the Prophet (blessings and peace be upon him) forbade sales involving gharar.” Gharar is anything whose reality is concealed from you and whose essence is hidden—whether the item is unknown or non-existent,