The Prophet of Allah ﷺ said, "If any of you knew that attending the prayer with me would earn him more than a fat sheep, or even two, he would surely come. Yet the reward he actually receives is far greater than that."
حدثنا معاذ بن هشام حدثني أبي عن قتادة عن الحسن عن أبي رافع
أن نبي الله ﷺ قال لو أن أحدكم يعلم أنه إذا شهد الصلاة معي كان له أعظم من شاة سمينة أو شاتين لفعل فما يصيب من الأجر أفضل
No references are available.
Its isnad is sahih. It appears in Jami al-Masanid wal-Sunan 7:420–421, taken from this very passage. Its meaning has already come at greater length under 7324, from the narration of Araj from Abu Hurairah. But with this exact wording and context, I have not found it anywhere else, except for a passing reference by Hafiz in Fath al-Bari 2:108, who attributed it to Harbi in his tafsir of the term "two hoof-trimmings" mentioned in the previous narration. However, the wording as it appears in Fath al-Bari is corrupted.