Jawamiʿ al-hikayat wa lawamiʿ al-riwayat 20: Mahmud's Youthful Strategy.

20

[IV. XX. 6.]
It is related by Abu-n Nasr 'Utbi in his work called Tarikh Yamini, that the King of Kabul made war upon the Muhammadans at the beginning of the career of Nasiru-d daula Subuktigin. When intelligence of this war was brought to the Amir Nasiru-d din, he called out his forces from Khurasan to oppose him. Sultan Mahmud was then about fourteen years of age. Amir Nasiru-d din summoned his officers and consulted with them upon the plan to be pursued. Amir Mahmud gave it as his opinion that the best course was to go in advance of the army and seek a strong place in the mountains, where they might make themselves secure, and from whence they might make nocturnal and unexpected assaults upon the enemy. They would thus prevent the foe from advancing against them, and distress him with incessant raids. The counsel was approved by all, and Amir Nasiru-d din advanced and occupied a position near Baghru. The King of Kabul marched thither with a countless army, and for some time the opposing forces encamped there.
One day a woman of the neighbourhood came to Amir Nasiru-d din and told him that there was a spring not far off in the mountains which had this property, that if filth was cast into it the sky became overcast, snow and storms followed, and the weather became so cold that no one in these parts could endure it. This cold and foul weather would last as long as the filth remained in the fountain. He sent and had some dirt thrown into the spring. Cold and stormy weather followed. The army of Hind was reduced to extremities, and the Musulmans were completely victorious.