Does a Muslim need to have an intention before fasting?
In the name of Allah, the Beneficent, the Merciful
For the obligatory fast during Ramadan, it is an obligation to have an intention to fast before the dawn prayer.
Umar ibn Al-Khattab reported: The Messenger of Allah, peace and blessings be upon him, said:
إِنَّمَا الْأَعْمَالُ بِالنِّيَّاتِ وَإِنَّمَا لِكُلِّ امْرِئٍ مَا نَوَى
Verily, deeds are only with intentions. Verily, every person will get rewarded only for what they intended.
Source: Sahih Bukhari 1, Grade: Sahih
Hafsa reported: The Prophet, peace and blessings be upon him, said:
مَنْ لَمْ يُجْمِعْ الصِّيَامَ قَبْلَ الْفَجْرِ فَلَا صِيَامَ لَهُ
Whoever does not have the intention to fast before dawn, then there is no fasting for him.
Source: Sunan At-Tirmidhi 730, Grade: Hasan
However, for voluntary fasting at other times, a Muslim may fast without having the intention before dawn prayer as long as he has not eaten or drank that day.
Aisha reported: The Messenger of Allah, peace and blessings be upon him, said to me one day:
يَا عَائِشَةُ هَلْ عِنْدَكُمْ شَيْءٌ
O Aisha, do you have anything?
She said, “O Messenger of Allah, I have nothing.” The Prophet said:
Verily, then I am fasting.
Source: Sahih Muslim 1154, Grade: Sahih
Success comes from Allah, and Allah knows best.