I'll fly away in it's original form was written by Albert E. Brumley in1929. I believe the 2nd verse is the verse you are referring to,


1.
Some glad morning when this life is o'er,
I'll fly away;
To a home on God's celestial shore,
I'll fly away.
CHORUS:
I'll fly away, O glory,
I'll fly away;
When I die, Hallelujah, by and by,
I'll fly away.

2.
When the shadows of this life have grown,
I'll fly away;
Like a bird from prison bars has flown,
I'll fly away.

3.
Just a few more weary days and then,
I'll fly away;
To a land where joys shall never end,
I'll fly away.

Who wrote the verse in I'll fly away that says something like: from these prison walls, I'll fly away.