The baby has dropped its toy, I'll .............
Options are:
pick up it.
pick it up
In this question I know the answer would be No. 2 — pick it up.
I just need any source, grammar book or dictionary, that affirms not to use the pronoun it after the phrasal verb pick up such as in the first answer.
In other words, a rule that prevent using the pronoun after the phrasal verb pick up.