"to recover his peace of mind"

There is no evidence to suggest that it is true that Sultan Mehmet II stabbed his wife. The story is a little reminiscent of the poem by Robert Browning, Porphyria’s Lover, in which the misguided narrator strangles his lover in order to preserve the moment of their love.

Porphyria worshiped me: surprise

Made my heart swell, and still it grew

While I debated what to do.

That moment she was mine, mine, fair,

Perfectly pure and good: I found

A thing to do, and all her hair

In one long yellow string I wound

Three times her little throat around,

And strangled her.

 

See the whole poem here.