Abū Hurayrah (RA) reports that the Prophet (SAW) said, “Faith has seventy-odd branches, the highest of them is the statement that none has the right to be worshipped save Allāh, and the least of them is removing something harmful from the road. Modesty is a branch of faith.” (Bukhārī, Muslim)
This ḥadīth explicitly tells us that faith is made up of statement of tongue, actions of limb, the articles of creed, and morals and manners. It also covers observing the rights of Allāh and being good to creation.
This ḥadīth mentions the highest branch of faith which is also the foundation and root: the statement that none has the right to be worshipped save Allāh. It is to be said with firm belief and sincerity. It mentions the lowest branch which is the removal of harmful things such as bones and thorns from the road. Consequently, other more important acts of kindness must also be branches of faith. Modesty has been mentioned because modesty gives life to faith, through it the servant leaves all vile actions and through it all good morals and manners are perfected. Allāh knows best.
The branches mentioned in the ḥadīth gather together all the requirements of this religion, inward and outward.
This ḥadīth also explicitly tells us that faith increases and decreases based on the strength or weakness of these branches. It is well-known that the faith of people differs greatly; whoever thinks that faith does not increase and decrease has ended up opposing not only the texts but also physical experience.