Treasury Regulations (26 C.F.R.)
26 CFR § 1.662(a)-1 — (a)-1 Inclusion of amounts in gross income of beneficiaries of estates and complex trusts; general.
There is included in the gross income of a beneficiary of an estate or complex trust the sum of:
(a) Amounts of income required to be distributed currently to him, and
(b) All other amounts properly paid, credited, or required to be distributed to him
Source: official text