How can the saying of the Prophet, peace and blessings be upon him, "The pens have been lifted, and the scrolls have dried" - meaning the destinies were written fifty thousand years ago - be reconciled with his hearing the sound of the pens scratching in the seventh heaven during the Mi'raj?

There is no contradiction between the hadiths. The scratching of pens that the Prophet, peace and blessings be upon him, heard on the Night of Mi'raj was the sound of the pens of the angels who write down the management of the world's affairs, and not the pen with which Allah wrote the destinies in the Preserved Tablet. There are several types of pens: 1. The first pen: which was created to write down the destinies in the Preserved Tablet before the creation of the heavens and the earth. 2. The pens of the angels: which write what is revealed to them for the management of the world. 3. The pen specific to revelation: with which Allah's revelation to His prophets is written. 4. The pens of destiny: which write the destinies of the children of Adam at their creation, when the soul is breathed into the fetus, and when the servant reaches maturity.

And Moses, peace be upon him, also heard the scratching of pens when the tablets were written for him.