Al-e-Imran (The House of Imran) Sura 3: Verse 139
"So lose not heart, nor feel distressed, for you shall gain mastery if you are true in faith."
Wahn means weakness, whether it concerns volition or action, or is of a physical or moral nature. In a hadith, we read that once the Prophet, peace be upon him, said to his companions that a time will come when Muslims will be reduced to 'froth and scum that rises above flood waters'. They asked about the reason for it whereupon he told them that they would have wahn in their hearts. 'What is wahn?' they asked him, and he replied, 'It is the love of the worldly life and the dislike of death' [Abu Dawud].
In the light of this hadith, we can say that wahn is the weakness in resolve and morale and the abject cowardice that leads to an abject failure of volition and action. This in turn stems from the love of worldly life and the fear of death that bars one from striving in the cause of truth. In the present verse, the phrase la tahinu (lose not heart) also has precisely this meaning. In other words, the defeat in the battle of Uhud should not demoralise you, break your spirit or disappoint you.
"Pondering Over The Qur'an: Surah Ali Imran" - Amin Ahsan Islahi