Commentary Mahaaraahulovaadasutta, no. 8.
Relevant Sutta passages:
Atha kho aayasmaa Raahulo saayanhasamaya.m pa.tisallaanaa vu.t.thito....
Then, at evening time, the venerable Rahula got up from solitude

"Ya.m ki~nci, Raahula, ajjhatta.m paccatta.m kakkha.la.m kharigata.m
upaadinna.m, seyyathida.m - kesaa lomaa nakhaa
whatever internally, and individually, is solid,
solidified, and clung to, namely: head hair, body hair, nails,
teeth...

Commentary:

bhagavataa pana aacikkhitakamma.t.thaanameva purebhattampi pacchaabhattampi
-- ``itipi ruupa.m anicca.m, itipi dukkha.m, itipi asubha.m, itipi
anattaa''ti aggi.m abhimatthento viya nirantara.m manasikatvaa
saayanhasamaye cintesi --

Rahula contemplated the meditation subject that was explained to him by the
Blessed One before and after his meal thus: ³Materiality truly is
impermanent, it truly is unsatisfactory, it truly is foul, it truly is
non-self². After he had contemplated this continuously (nirantara.m), just
as someone who desires to have light, the following thoughts occurred to him
towards evening:

``aha.m upajjhaayena aanaapaanassati.m bhaavehiiti vutto , tassa vacana.m
karissaami aacariyupajjhaayaana~nhi vacana.m akaronto dubbaco naama hoti.

³Since my preceptor has told me (aha.m vutto) to develop mindfulness of
breathing I shall be obedient (vacana.m karissaami). If I don¹t follow what
my teachers and preceptors say, I am indeed obstinate ( dubbaco, difficult
to speak to).

`dubbaco raahulo, upajjhaayassapi vacana.m na karotii'ti ca garahuppattito
kakkha.lataraa pii.laa naama natthii''ti bhaavanaavidhaana.m pucchitukaamo
bhagavato santika.m agamaasi. ta.m dassetu.m atha kho aayasmaa raahulotiaadi
vutta.m.

Nothing is more oppressive and harsh than receiving the reproach, Rahula who
is obstinate does not follow up the words of his preceptor. ³
He visited the Blessed One personally because he was eager to ask about the
ways of mental development. It was said (by Ananda ), atha kho aayasmaa
raahulo, then, (at evening time,) the venerable Rahula (got up from
solitude) etc.

tattha pa.tisallaanaati ekiibhaavato. ya.mki~nci raahulaati kasmaa?
bhagavaa aanaapaanassati.m pu.t.tho ruupakamma.t.thaana.m kathetiiti. ruupe
chandaraagappahaanattha.m.

Then, as to the word, pa.tisallaanaa, (having got up), this means, from
solitude (ekiibhaava, being alone).
As to the words, ya.mki~nci raahulaa, whatever, Rahula (is internal, etc.),
why is this said? When he asked the Blessed One about Mindfulness of
Breathing, The Blessed One spoke about the meditation subject of
materiality, so that he (Rahula) would abandon his attachment to materiality
(attha.m, with the aim).

****
Remarks, questions: na karissaami: Burmese and Siamese manuscript omit : na.
I shall follow the words, be obedient... I erased the na in my text, it
makes more sense.
As to:
garahuppattito kakkha.lataraa pii.laa naama natthii''ti , not sure. I
compared with my Thai text. This came out. A comparative. I like to be
corrected, please.
Nina.