Reference for Sanhedrin 221:13
כשחטאו ישראל אמר לו לא כך אמרת לי ארך אפים לצדיקים
What did Moses see?<span class="x" onmousemove="('comment',' This verse follows the enumeration of God's thirteen Attributes. Which of these did he see, that he hastened to bow and worship? ');"><sup>36</sup></span> — R. Hanina b. Gamala<span class="x" onmousemove="('comment',' Var. lec. 'Gamaliel.' ');"><sup>37</sup></span> said: He saw long-suffering [as one of His attributes].<span class="x" onmousemove="('comment',' Ibid. 7. ');"><sup>38</sup></span> The Rabbis say: He saw [His attribute of] truth.<span class="x" onmousemove="('comment',' Ibid. 7. ');"><sup>38</sup></span> It has been taught in agreement with the one who holds that 'he saw long-suffering,' viz.,<span class="x" onmousemove="('comment',' Lit., 'For it has been taught.' ');"><sup>39</sup></span> When Moses ascended on high, he found the Holy One, blessed be He, sitting and writing 'long-suffering'. Said he to Him, 'Sovereign of the Universe! Long-suffering to the righteous?' He replied, 'Even' to the wicked.' He urged, 'Let the wicked perish!' 'See now what thou desirest,' was His answer.<span class="x" onmousemove="('comment',' It is an ill-advised request, which thou wilt revoke at a future occasion, viz., at the sin of the Golden Calf. ');"><sup>40</sup></span> 'When Israel sinned,' He said to him, 'didst thou not urge Me, [Let Thy] long-suffering be for the righteous [only]?'