Numerous reports in the hadith and exegetical literature of both Sunni and Shiʿa traditions caution against speaking about the Qur’an without proper knowledge. Over time, these warnings contributed to the formation of a widely accepted notion known as "the prohibition of tafsīr bi’l-raʾy (interpretation based on personal opinion)." Today, this notion is so deeply entrenched that its historical development and widespread acceptance have rarely been scrutinized. This study addresses critical yet overlooked questions surrounding its origins and evolution. 
The research explores whether the existing reports on tafsīr bi’l-raʾy authentically reflect the Prophetic stance and whether the position of the Prophet (PBUH) on this matter can even be determined from these texts. Additionally, it investigates the timeline and contextual factors behind the emergence, development, and eventual dominance of the notion of its prohibition. Employing a historical-discursive approach, the study meticulously analyzes early exegetical and hadith reports. The findings challenge conventional assumptions, demonstrating that the available evidence does not support attributing a definitive stance on tafsīr bi’l-raʾy to the Prophet (PBUH). Moreover, the notion of its prohibition cannot be conclusively traced to the first century AH. Even Shiʿi reports that frame the prohibition as a divine tradition (ḥadīth qudsī) are datable only to the late second century AH. 
A critical examination of Sunni sources through isnād analysis reveals that the relevant reports lack reliable transmission chains prior to the generation of the atbāʿ al-tābiʿīn, suggesting their probable formulation during the mid-second century AH—a period marked by intense theological debates between Ahl al-Raʾy and Ahl al-Ḥadīth. Early discussions revolved around "speaking without knowledge" or "giving opinions" about the Qur’an, with the specific concept of tafsīr bi’l-raʾy crystallizing later. By the third century AH, hadith scholars redefined these ideas, culminating in the pervasive notion of tafsīr bi’l-raʾy as a prohibited practice. 
In Shiʿi sources, the discourse on tafsīr bi’l-raʾy reflects the traditionalist stance of Shiʿi scholarship from the era of Imam Jaʿfar al-Ṣādiq  onward. This tradition positioned itself in opposition to rationalist approaches (Ahl al-Raʾy) and analogical reasoning (qiyās), vehemently rejecting subjective interpretation. The Shiʿi narratives that elevate the prohibition to the status of a divine saying emerge no earlier than the late second century AH, aligning with broader intra-Islamic polemics of the time.