Originally from here.

CANTO 28

Whilst eagerly I fix on him my gaze,
He ey’d me, with his hands laid his breast bare,
And cried; “Now mark how I do rip me! lo!
“How is Mohammed mangled! before me
Walks Ali weeping, from the chin his face
Cleft to the forelock; and the others all
Whom here thou seest, while they liv’d, did sow
Scandal and schism, and therefore thus are rent.
A fiend is here behind, who with his sword
Hacks us thus cruelly, slivering again
Each of this ream, when we have compast round
The dismal way, for first our gashes close
Ere we repass before him.  But say who
Art thou, that standest musing on the rock,
Haply so lingering to delay the pain
Sentenc’d upon thy crimes?”—“Him death not yet,”
My guide rejoin’d, “hath overta’en, nor sin
Conducts to torment; but, that he may make
Full trial of your state, I who am dead
Must through the depths of hell, from orb to orb,
Conduct him.  Trust my words, for they are true.”

More than a hundred spirits, when that they heard,
Stood in the foss to mark me, through amazed,
Forgetful of their pangs.  “Thou, who perchance
Shalt shortly view the sun, this warning thou
Bear to Dolcino: bid him, if he wish not
Here soon to follow me, that with good store
Of food he arm him, lest impris’ning snows
Yield him a victim to Novara’s power,
No easy conquest else.”  With foot uprais’d
For stepping, spake Mohammed, on the ground
Then fix’d it to depart.  Another shade,
Pierc’d in the throat, his nostrils mutilate
E’en from beneath the eyebrows, and one ear
Lopt off, who with the rest through wonder stood
Gazing, before the rest advanc’d, and bar’d
His wind-pipe, that without was all o’ersmear’d
With crimson stain.

—

Originally from here.

CliffsNotes on Canto XXVIII (28)

The canto opens with Dante wondering how to describe the sinners in the ninth chasm. This is the place of the Sowers of Discord and Scandal, and the Creators of Schism within the papacy. He warns that the punishment in this part of Hell is bloody and grotesque. Indeed, the sinners in the ninth chasm are damned to walk around the chasm until they arrive at a devil who slashes them with a long sword, according to the nature of their sin (cp. Matthew 24:51).

The first one Dante sees is Mahomet, disemboweled, who tells him that his son-in-law, Ali, is in the same condition and that all the others are horribly mangled in some manner. As they circle the chasm, the wounds heal, but when they complete the circle, the wounds are renewed by a devil with a sword.

Mahomet explains that these sinners were responsible for scandal and rift, and therefore, they are torn apart as they tore others apart in life. Mahomet asks Dante to tell Fra Dolcino, who is still alive, to store food for the winter or risk joining him in the chasm. After asking Dante to warn his friend, Mahomet moves on.

In keeping with the theme of Divine Retribution that runs throughout Inferno, the sinners in the ninth chasm, the Sowers of Discord, are brutally split and mutilated, just as they split and mutilated aspects of religion, politics, or kinsmen. Each sinner is punished according to degree of sin, as well as suffering punishment specifically geared toward their particular sin.

Dante obviously sees Mahomet as one of the chief sinners responsible for the division between Christianity and Islam. Dante blames Mahomet’s successor, Ali, as well. Dante describes these two shades as being split in two, just as he feels they split the church.