Sruti, the vedas, and more specifically, the Upanishads, define Sruti. One of the three Prasthanas accepted by all Hindus as the authoritative texts, The Brahma Sutras, section 2.1. says (Swami Vireswarananda translator, https://www.wisdomlib.org/hinduism/book/brahma-sutras/d/doc63014.html)
Adhikarana summary: Refutation of Smritis that are not based on the Srutis
स्मृत्यनवकाशदोषप्रसङ्ग इति चेत्, न,
अन्यस्मृत्यनवकाशदोषप्रसङ्गात् ॥ १ ॥
smṛtyanavakāśadoṣaprasaṅga iti cet, na,
anyasmṛtyanavakāśadoṣaprasaṅgāt || 1 ||
smṛti-anavakāśa-doṣaprasaṅgaḥ—There would result the defect of leaving no scope for certain Smritis; if it be said no; because there would result the defect of leaving no scope to some other Smritis.
- If it be said that (from the doctrine of Brahman being the cause of the world) there would result the defect of leaving no scope for certain Smirits, (we say) no; because (by the rejection of that doctrine) there would result the defect of leaving no scope for some other Smritis.
In the last chapter it has been shown that the Sankhyan view is not based on scriptural authority. Now its authority even as a Smriti is denied and refuted.
If the doctrine of the Pradhana is rejected, then the Sankhya Smriti, propounded by a great seer like Kapila and acknowledged by other great thinkers, would cease to be authoritative : hence it is but reasonable that the Vedanta texts be so interpreted as to preserve the authorilativeness of this Smriti and not contradict it in toto , So says the opponent. The Sutra answers this by saying that if the doctrine of Brahman being the cause of the world be rejected to accommodate the Sankhya Smriti, which goes counter to the Srutis, then by that rejection many other Smritis like the Manu Smriti, which are based on the Srutis and therefore more authoritative, and, which also propound the doctrine of Brahman, an intelligent principle, being the cause of the world, would find no scope. So between the two it is desirable that the Smritis which go counter to the Vedas be rejected.
Brahma-Sutra 2.1.2: Sanskrit text and English translation.
इतरेषां चानुपलब्धेः ॥ २ ॥
itareṣāṃ cānupalabdheḥ || 2 ||
itareṣāṃ—Of the others; ca—and; anupalabdheḥ—there being no mention.
- And there being no mention (in the scriptures) of the other entities, (i.e. the categories beside the Pradhana), (the Sankhya system cannot be authoritative).
Even accepting the Pradhana of the Sankhyas for argument’s sake—for the Vedantins also recognize Maya as the cause of the world, the difference between the two being that the Pradhana according to the Sankhyas is an independent entity, whereas Maya is a dependent entity, being a power of Brahman— yet there is no mention of the other categories of the Sankhyas anywhere in the Vedas. Hence the Sankhya philosophy cannot be authoritative.
and the next topic says:
Adhikarana summary: Refutation of the Yoga philosophy
Brahma-Sutra 2.1.3: Sanskrit text and English translation.
एतेन योगः प्रत्युक्तः ॥ ३ ॥
etena yogaḥ pratyuktaḥ || 3 ||
etena—By this; yogaḥ—the Yoga philosophy; pratyuktaḥ—is (also) refuted.
- By this the Yoga philosophy is (also) refuted.
After the refutation of the Sankhyas, who recognize an independent entity called the Pradhana as the cause of the world, this Sutra refutes the Yoga Smriti, which also recognizes a separate entity called the Pradhana as the First Cause, though unlike the Sankhyas they recognize an Iswara who directs this inert Pradhana in its creative evolution. The Yoga system is spoken of in Upanishads like the Svetasvatara. It helps concentration of the mind, which is necessary for the full comprehension of Brahman, and as such it is a means to Knowledge. So this Smriti, being based on the Siutis is authoritative. But it also recognizes the Pradhana, which therefore is the First Cause—so says the opponent. This Sutra says that the arguments given in the last Sutra refute also the Yoga Smriti, for it also speaks of a Pradhana and its products which are not to be found in the Srutis. Though the Smriti is partly authoritative, yet it cannot be so with respect to that part which contradicts the Srutis. There is room only for those portions of the Smriti as do not contradict the Srutis.
and in Brahma Sutras 1.2.25:
Brahma-Sutra 1.2.25: Sanskrit text and English translation.
स्मर्यमाणमनुमानं स्यादिति ॥ २५ ॥
smaryamāṇamanumānaṃ syāditi || 25 ||
smaryamāṇaṃ—Described in the Smriti; anumānaṃ—indicatory mark; syāt—must be; iti—because.
- Because that (cosmic form of the Supreme Lord) which is described in the Smriti must be an indicatory mark (from which we arrive at the meaning of this Sruti text under discussion).
The Smritis are interpretations of Sruti texts. So where a doubt arises as to the meaning of a Sruti the former may be consulted to throw light on the subject. The Smriti describes the cosmic form of the Supreme Lord as,
“He whose mouth is fire, whose head is heaven, . . . whose ears are the regions—salutation to Him, whose body is the universe”,
which agrees with the description in the text under discussion. Hence we have to conclude that the Highest Lord is referred to in the text.
Smriti can be accepted as authoritative so long as it does not contradict Sruti. Smriti which contradicts Sruti is to be rejected.