What is the evidence for supplicating the Qur'an's completion in prayer with qunut?

Supplication upon completing the Quran is recommended outside of prayer. Regarding its recommendation within prayer, scholars have differed. Imam Ahmad, Sufyan ibn Uyaynah, and the people of Mecca held it to be recommended, citing the practice of the people of Mecca as evidence. العلامة Ibn Baz supported this view, stating that he was unaware of any disagreement among the Salaf on this matter. He analogized it to supplication outside of prayer and cited the practice of Anas ibn Malik, who would gather his family and supplicate upon completing the Quran. Thus, the matter is recommended and there is no harm in it.