宋高僧傳 1.56

1.56

又天寶中，西蕃、大石、康三國帥兵圍西涼府，詔空入，帝御于道場。空秉香罏，誦《仁王》密語二七遍，帝見神兵可五百員在于殿庭，驚問空。空曰：「毘沙門天王子領兵救安西，請急設食發遣。」四月二十日果奏云：「二月十一日。城東北三十許里，雲霧間見神兵長偉，鼓角諠鳴，山地崩震，蕃部驚潰。彼營壘中有鼠金色，咋弓弩弦皆絕。城北門樓有光明天王怒視，蕃帥大奔。」帝覽奏謝空，因勅諸道城樓置天王像，此其始也。

Moreover, during the Tianbao era, the three countries of Tubo, the Arabs, and Kang led troops to besiege the prefecture of Xiliang. Amoghavajra was summoned inside, and the emperor presided over the ritual arena. Holding an incense burner, Amoghavajra recited the secret words of the Benevolent Kings [Sūtra] fourteen times. The emperor saw divine soldiers, perhaps five hundred strong, in the courtyard of the hall, and in alarm asked Amoghavajra. Amoghavajra said: "The prince of Heavenly King Vaiśravaṇa is leading troops to rescue Anxi; please swiftly set out food and dispatch them." On the twentieth day of the fourth month, a memorial indeed arrived saying: "On the eleventh day of the second month, about thirty li northeast of the city, amid the clouds and mist were seen divine soldiers, tall and mighty, drums and horns blaring loudly, and the mountain terrain quaking and crumbling, so that the barbarian forces scattered in panic. In their camps, there were golden-colored rats that gnawed and severed all the strings of their bows and crossbows. On the tower of the northern city gate, a radiant Heavenly King glared in anger, and the barbarian commanders fled in great disarray." The emperor read the memorial and thanked Amoghavajra, subsequently ordering that images of the Heavenly King be placed on the gate towers of cities in all circuits; this was the beginning of it.