Having the intention to observe Sawm during the night before dawn each day is Wajib (obligatory) according to Shari`ah.
Hafsah (may Allah be pleased with her) said that the Prophet (peace be upon him) stated:
He who does not determine to fast before dawn does not fast.
(Related by Ahl-ul-Sunan [authors of Hadith compilations classified by jurisprudential themes]) The heart is the place to determine intention.
`Umar (may Allah be pleased with him) said that the Prophet (peace be upon him) stated:
The reward of deeds depends upon the intentions.
(Agreed upon by Al-Bukhari and Muslim) Therefore, pronouncing the intention to observe Sawm or perform Salah (Prayer) is Bid`ah (innovation in Islam) which has no evidence. People falsely attribute this act to the Madh-hab (School of Jurisprudence) of Imam
Al-Shafi`y (may Allah be merciful to him). There is not a single text stating that intention should be pronounced verbally. This is proved by Imam
Ibn Al-Qayyim (may Allah be merciful to him) in his book Zad-ul-Ma`ad. Hence, people of that Masjid (mosque) should abandon verbal pronunciation of intention. Adhering to Sunnah (whatever is reported from the Prophet) is an act full of goodness and blessings.