The 'sweetness of faith' is metaphorical, not tangible and felt on the tongue
27-4-2015 | IslamWeb
Question:
Assalamu alaikum, your website is very helpful and may Allaah continue to assist you in doing this great job. Please I need a clarification regarding the sweetness of iman. I know the ahadith that specifies the qualities needed to obtain such sweetness. However, it was said that there was a saint, who used to say that he experienced so much pleasure in taking the name of Allah that his mouth would become sweet. He would take an oath that his mouth had indeed become sweet. Is this sweetness metaphorical or an actual taste perceived in the mouthɁ Please elaborate more on this, Jazakallahu khairan.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ʻalayhi wa sallam, is His Slave and Messenger.
We do not know about the story to which you have referred in the question. Many of the stories told about the Karaamaat (marvels) of Allaah's Awliyaa’ (friends) may not be true and are in fact lies and fabrications, especially those cited in the writings of the late Sufi scholars such as the Tabaqaat of Ash-Shaʻraani, the Tabaqaat of Wadd Dhayfullaah and the like. In fact, some of those false stories oppose the teachings of the Islamic Shareeʻah to begin with, and the pious people about whom these false stories are tailored may have nothing to do with what is attributed to them.
In any case, the scholars’ statements about the explanation of the sweetness of faith indicate that it is a spiritual sweetness, and not a tangible one that the person finds on his tongue like the sweetness of food and drink. Al-Haafith Ibn Hajar 
wrote, “The expression "sweetness of faith" comprises a loose metaphor; it likens the believer's desire for faith to something sweet.” [Fat-h Al-Baari]
An-Nawawi wrote, “Scholars explained that "sweetness of faith" means finding pleasure in performing acts of worship and righteous deeds, joyfully enduring the hardships in order to earn the pleasure of Allaah and His Messenger, sallallaahu ʻalayhi wa sallam, and favoring that to all worldly pleasures, while having love for Allaah and translating that love into obedience to Him, avoiding disobeying Him and loving His Messenger, sallallaahu ʻalayhi wa sallam.” [Sharh Saheeh Muslim]
Al-Munaawi wrote, “The sweetness of faith means finding pleasure and joy in obeying Allaah, enduring hardships in order to earn His pleasure and that of His Messenger, and favoring that to all worldly pleasures.” [Faydh Al-Qadeer]
Allaah Knows best.