The Prophet ﷺ said, "Beware of suspicion, for suspicion is the most false form of speech. Do not spy on one another, do not pry into each other's affairs, do not envy one another, do not inflate prices against one another, do not turn your backs on one another, and do not hate one another. Be servants of Allah, brothers to each other."
حدثنا حسين بن علي الجعفي عن زائدة عن عبد الله بن ذكوان عن عبد الرحمن الأعرج
عن النبي ﷺ قال إياكم والظن فإن الظن أكذب الحديث لا تجسسوا ولا تحسسوا ولا تنافسوا ولا تناجشوا ولا تدابروا ولا تباغضوا وكونوا عباد الله إخوانا
Its chain of transmission is sahih. Zaida is Ibn Qudama. Abdullah bin Zakwan is Abu Zinad, and the hadith's beginning only has already appeared at 7333 from Sufyan bin Uyayna, from Abu Zinad. We have already pointed out many places where it is cited in full, in the Sahihayn and in the Musnad, including this narration. Hafiz has discussed its wording at length in Fath al-Bari 10:401–405.His saying, "and do not practice najsh," is spelled with nun, jim, and shin (with a dot), from najsh. This means bidding up the price of goods without wanting to buy them, so that someone else falls into paying more for them. The prohibition of this has already appeared several times, including at 6451, 7247, and 7713. This wording is established in this hadith as recorded by Bukhari 10:404, through the narration of Malik from Abu Zinad. Hafiz says there that what appears in all the narrations from Malik is the wording "and do not compete with one another," with fa and sin (without a dot). He then mentions the narrations in the Muwattas, and the narration of Muslim through Malik's route. He then mentions that Muslim also recorded it with the same wording through the narration of Suhayl bin Abu Salih, from his father, from Abu Hurairah. Then he says, "But he also recorded it through the route of Amash, from Abu Salih, with the wording 'and do not practice najsh,' as it occurs in Bukhari, and also through the route of Abu Saeed, freedman of Amir bin Kurayz, with the same wording. So the wording differs both regarding what is attributed to Abu Hurairah and regarding what is attributed to Abu Salih from him, so it would not be surprising if the wording also differs regarding what is attributed to Malik."Hafiz, may Allah have mercy on him, forgot this narration in the Musnad, which contains both wordings together, "do not compete with one another" and "do not practice najsh." So this is not a case of disagreement regarding what is attributed to Abu Hurairah or to anyone else. Rather, it is simply that some parts of the hadith's wording were sometimes left out, sometimes one phrase and sometimes the other. Perhaps Abu Hurairah narrated it on different occasions, and the shortening came from him, which is what I consider more likely. Or the shortening may have come from a later narrator, and either way the matter is close.