Hawzah News Agency – Imam al-Sadiq peace be upon him says:

حرامٌ على قلوبِكُم أنْ تعرِفَ حَلاوةَ الإيمانِ حتّى‏ تَزهَدَ في الدّنيا.

'It is prohibited for your hearts to experience the sweetness of faith until they abstain from this world [i.e. its pleasures].'

Source: al-Kafi, v. 2, p. 128, no. 2