Commentary to the Greater Discourse to Rahula, M, sutta 62., no 2.
The relevant sutta passage:
<Thus have I heard. At one time the Blessed One stayed in the garden
of Anathapindika, in Jeta's forest, near Savatthi. Then, when it was
morning, the Blessed One, having dressed and taken his robe and bowl,
entered Saavatthi for alms. Venerable Raahula too, when it was
morning, having dressed and taken his robe and bowl, followed the
Blessed One closely from behind. And then the Blessed one, looking
back towards Rahula, addressed him:

"Rahula, whatever form, - past, future or present, internal or
external, gross or subtle, base or exalted, whether it is far or
near, - all form should be seen as it really is with right wisdom in
such a way: "This is not mine, I am not this, this is not me".

"Form only, Blessed One? Form only, Sugata [the Well-gone]>

Commentary:
We read that the Buddha considered that he should not neglect Rahula, that
he should urge him so that his defilements would not ruin the jewel of his
síla. The Buddha turned back with the "great elephant's look" (with his
whole body), such as Buddhas always do. Ananda referred to "Lucky Rahula"
(Raahula baddha)[1] when he said, "Atha kho Bhagavaa apaloketvaa" [N:as in
the sutta], "then the Buddha, after he had looked back... " At that time
the Buddha turned around in that way.
We read further on in the Commentary:<As to the words, ya.m ki~nci ruupa.m,
whatever are ruupas (material phenomena), this is explained in detail in the
Visuddhimagga, khandha niddesa. As to the words, n'eta.m mama, this is not
myself, this has been explained in the "Greater Discourse on the Elephant's
Footprint" (M 28).
Therefore Rahula asked, " ruupa.m eva nu kho Bhagavaa, only materiality,
Lord? To Rahula occurred the methods of teaching (naya), because he heard,
materiality is not mine, this am I not, this is not myself. The Buddha said,
you ought to see all material phenomena with insight wisdom (vipassanaa
pa~n~naa). How should he practise with regard to feelings etc.? Since Rahula
was established in this method (of teaching) he asked that question. Rahula
was clever in the methods of teaching. When the Buddha said, "one should not
act like this", he realized even a hundred or a thousand methods, of "one
should act like this, one should not act like that". And even so, when the
Buddha said, "one should act like this", he considered in that way according
to many methods.>
[1] Note: Rahula was called "lucky", baddha, because he was the Buddha's son
and he attained arahatship.
Nina