PREPOSITIONS. In with the verbalIn is used with a verbal to signify "in the act of" or "while."
“He raves in saying nothing.
“When you cast
Your stinking greasy caps in hooting at
“Mine eyes, the outward watch
Whereto my finger like a dial's point
Is pointing still, in cleansing them from tears.
“The fire that mounts the liquor till't run o'er,
In seeming to augment it, wastes it.
“And may ye both be suddenly surprised
By bloody hands in sleeping on your beds.
It is probable, as the last example suggests, that these verbals are nouns after which "of" is sometimes expressed. Hence "in sleeping" may simply be another form of "a-sleeping." But the in brings out, more strongly than the a-, the time in which, or while, the action is being performed. It is also probable that the influence of the French idiom, "en disant ces mots," tended to mislead English authors into the belief that in was superfluous, and that the verbals thus used were present participles. (See also 93.) In is used thus with a noun:
“As patches set upon a little breach
Discredit more in hiding of the fault.
“Wept like two children in (during) their deaths' sad stories.
“(These blazes) giving more light than heat, extinct in both,
Even in their promise, while it is a-making.