During the Mahabharata War, the boundaries between Dharma and Morality blurred several times. When the Kaurava commander, Guru Dronacharya, attacked the Pandava army like death on the battlefield of Kurukshetra, defeating him seemed impossible. In such a situation, Lord Krishna devised a strategy that even the truthful Yudhishthira had to resort to an act of "Adharma." Let us examine this incident of deceit and dharma, which occurred on the 15th day of the Mahabharata War:

When Guru Dronacharya became invincible,
after Bhishma Pitamah died on his deathbed, Guru Dronacharya became the commander-in-chief of the Kaurava army. His divine weapons and war skills created havoc in the Pandava army. As long as Dronacharya had weapons in his hands, it was impossible to defeat him in battle. Seeing the Pandavas' defeat certain, Shri Krishna understood that there was only one way to stop Drona – to break him mentally due to his love for his son.

Naro va Kunjaro va: Krishna's Diplomacy
Following Krishna's advice, Bhima killed the elephant named Ashwatthama, belonging to King Indravarma of Malwa. Bhima then shouted from the battlefield, "Ashwatthama is dead!"

When this news reached Guru Drona, he was incredulous. He knew that Yudhishthira was the only one of the Pandavas who never told a lie. Dronacharya asked Yudhishthira to confirm the truth, asking if his son Ashwatthama had truly been killed.

Yudhishthira's half truth and blowing of the conch
Yudhishthira replied: "Ashwatthama hatah" (Ashwatthama is killed), but immediately after this he said in a low voice—"naro va kunjaro va" (human or elephant, I do not know).

As soon as Yudhishthira said "Naro va Kunjaro va," Lord Krishna immediately blew his Panchajanya conch. The intense sound of the conch drowned out Yudhishthira's subsequent words, and Dronacharya could only hear that his son, Ashwatthama, had been killed.

Distressed by grief for
his son, Guru Dronacharya abandoned his bow and arrows on the battlefield and sat down in deep meditation. Seizing this opportunity, Drupada's sons and Dhristadyumna killed Dronacharya with their swords.

PC: Acharyaprashant