The Quran

ما جَعَلَ اللَّهُ لِرَجُلٍ مِن قَلبَينِ في جَوفِهِ ۚ وَما جَعَلَ أَزواجَكُمُ اللّائي تُظاهِرونَ مِنهُنَّ أُمَّهاتِكُم ۚ وَما جَعَلَ أَدعِياءَكُم أَبناءَكُم ۚ ذٰلِكُم قَولُكُم بِأَفواهِكُم ۖ وَاللَّهُ يَقولُ الحَقَّ وَهُوَ يَهدِي السَّبيلَ

Muhammad Asad

NEVER has God endowed any man with two hearts in one body:¹ and [just as] He has never made your wives whom you may have declared to be "as unlawful to you as your mothers' bodies" [truly] your mothers,² so, too, has He never made your adopted sons [truly] your sons:³ these are but [figures of] speech uttered by your mouths - whereas God speaks the [absolute] truth:⁴ and it is He alone who can show [you] the right path.

Lit., "within him". In the first instance, this connects with the preceding passage, implying that man cannot be truly conscious of God and at the same time defer to the views of "the deniers of the truth and the hypocrites" (Razi) Beyond this, however, the above sentence forms a conceptual link with the sequence, which states that it is against the God-willed laws of nature - and, therefore, unreasonable and morally inadmissible - to attribute to one and the same person two mutually incompatible roles within the framework of human relationships (Zamakhshari).
This is a reference to the pre-islamic Arabian custom called zihar, whereby a husband could divorce his wife by simply declaring, "Thou art [henceforth as unlawful] to me as my mother's back", the term zahr ("back") being in this case a metonym for "body". In pagan Arab society, this mode of divorce was considered final and irrevocable; but a woman thus divorced was not allowed to remarry, and had to remain forever in her former husband's custody. As is evident from the first four verses of surah 58 (Al-Mujadalah) - which was revealed somewhat earlier than the present surah - this cruel pagan custom had already been abolished by the time of the revelation of the above verse, and is mentioned here only as an illustration of the subsequent dictum that the "figures of speech [lit., "your sayings"] which you utter with your mouths" do not necessarily coincide with the reality of human relations.
I.e., in the sense of blood relationship: hence, the marriage restrictions applying to real sons - and, by obvious implication, daughters as well do not apply to adoptive children. This statement has a definite bearing on verses 37 ff. below.
Sc., by bringing into being the factual, biological relationship of parent and child in distinction from all man-made, social relationships like husband and wife, or foster-parent and adoptive child. In this connection it should be borne in mind that the Qur'an frequently uses the metaphor of God's "speech" to express His creative activity.