Why count prayers on a string
Repeating a short prayer many times is a feature of several religions, and the practical problem is the same everywhere: how to keep count without losing your place. A string of beads solves it. One bead is held for each repetition, and the hand moves along the string while the mind stays on the words.
Historians disagree about how and where the practice began, and about how far the traditions influenced one another. Strings of beads for counting are old in South Asia, and similar devices appear in later Christian and Muslim use, but the direction of borrowing, if there was any, is uncertain. What can be described with more confidence is how each tradition uses its beads today.
The Christian rosary
The Catholic rosary is built around the Hail Mary, with the Our Father and Glory Be placed between sets. A standard rosary has five decades, each made of ten small beads for Hail Marys with one larger bead before each decade. Five decades come to 50 Hail Marys, and the full set of beads is a loop with a short tail ending in a crucifix.
The medieval background helps explain the numbers. Lay people who could not read the 150 Psalms used to say 150 Our Fathers, strung on cords sometimes called paternoster beads. Over time the Hail Mary took over, and the 150 became three sets of fifty, each set a “chaplet”. The number of 150 therefore reflects the Psalter, and not a numerical principle in itself.
The rosary is also a way of meditating on events in the life of Jesus and Mary, called mysteries. For centuries there were 15, grouped in threes of five: joyful, sorrowful and glorious. In 2002 Pope John Paul II added five Luminous mysteries, making 20. That means a complete round of all four sets covers 20 decades, or 200 Hail Marys, though people usually pray one set at a time.
A later legend credits Saint Dominic with receiving the rosary from the Virgin Mary. Many historians regard that story as a pious tradition with little early evidence, and they see the rosary as developing gradually between the twelfth and sixteenth centuries.
Other Christian traditions have their own forms. Eastern Orthodox and some Eastern Catholic Christians use a knotted prayer rope, often with the Jesus Prayer, and the number of knots varies by custom. Some Anglicans and other Protestants have adopted prayer beads in recent decades, with arrangements that differ from group to group.
The Islamic misbaha and tasbih
The Muslim prayer string is called a misbaha, sibha or tasbih in different regions, from the word for glorifying God. The beads count short phrases of remembrance, called dhikr. A common practice after the daily ritual prayers is to say “Subhan Allah” (glory be to God), “Al-hamdu lillah” (praise be to God) and “Allahu akbar” (God is greatest), reported in the hadith literature as 33, 33 and 34 times, which totals 100.
Strings usually have 99 beads, often in three sections of 33 with a marker, or 33 beads that are cycled three times, or sometimes 100 beads. The 99 is tied to the traditional count of the divine names, an idea described under ninety-nine names. Some Muslims prefer to count on the fingers, and views on beads differ by region and school. The beads are an aid, not one of the obligatory duties of the faith.
The Buddhist mala
The mala is common in Buddhist and Hindu practice, where it is used to count repetitions of a mantra or the name of a deity or Buddha. The usual number of beads is 108, with shorter strings of 54 or 27 for convenience. A larger bead, often called the guru bead, marks the start so the reciter knows when a round has been completed and turns back without crossing it.
Why 108? Several explanations are offered, and none is accepted by all schools. Writers have linked it to lists of mental states, to astronomical ideas, and to arithmetic curiosities such as 108 being 1 × 2² × 3³ (that is, 1 × 4 × 27). These are best read as traditional reasons, and the question is explored in the article on the number 108.
What the three share and where they differ
All three are counting aids that became objects of devotion in their own right. The numbers they use are practical to some degree: a rosary of fifty beads is easy to hold, and a string of 33 or 99 can be cycled quickly.
They differ in purpose and meaning. The rosary joins repetition to meditation on a story. The misbaha counts phrases of remembrance and, through its 99, recalls a list of names. The mala often supports a concentration practice, and its 108 is part of a wider set of traditions about that number.
None of this implies that the number of beads has any effect of its own. For the people who use them, the point is attention and habit, and the beads are a way to keep that attention steady. Outsiders can see them as an example of ritual numbers: numbers fixed by custom and repeated because they are part of a shared practice.