Sayyiduna Jarir bin Abdullah (may Allah be pleased with him) said: I pledged allegiance to the Messenger of Allah (peace and blessings be upon him) on establishing prayer, giving zakat, and being sincere to every Muslim.
Hadith Referenceسنن دارمي / من كتاب البيوع / 2576
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح والحديث متفق عليه، [مكتبه الشامله نمبر: 2582]
Hadith Takhrijاس روایت کی سند صحیح اور حدیث متفق علیہ ہے۔ دیکھئے: [بخاري 57] ، [مسلم 56] ، [أبويعلی 7503] ، [ابن حبان 4545] ، [الحميدي 813]
Brief Explanation
(Commentary on Hadith 2575)
From this hadith, it is understood that performing prayer (salah), giving zakat upon being sahib-e-nisab (possessor of the minimum amount liable for zakat), and wishing well for every Muslim are among the obligations (wajibat) of every Muslim. Especially in matters of buying and selling, one should demonstrate goodwill towards one's Muslim brother at the time of transaction; one should not engage in unlawful trade through deceit and fraud.
The very purpose of mentioning this hadith in the Book of Transactions (Kitab al-Buyu‘) is this.
From this, the insight and understanding of fiqh (Islamic jurisprudence) of Imam Darimi rahimahullah becomes evident.