In the Gemara Berakhot on folio 11b, the text records a dispute regarding the proper opening for the second blessing associated with the recitation of the Shema. The central question involves a choice between two distinct liturgical formulas: Ahaba Rabba and Ahavat Olam. This disagreement highlights different traditions concerning the language used to introduce this significant portion of the prayer service.
The commentary of Tosafot, specifically in the discussion beginning with the words "Verabbanan Amri Ahavat Olam," clarifies how this matter was ultimately settled. To address the different opinions, the Sages established a practice that incorporates both versions into the daily liturgy. They instituted that Shacharit, the morning service, should feature the recitation of Ahaba Rabba, while Arvit, the evening service, should utilize the formula of Ahavat Olam. Through this arrangement, both traditional openings are preserved and given a designated place within the cycle of daily prayer.