The Quran

يا أَيُّهَا النَّبِيُّ إِذا جاءَكَ المُؤمِناتُ يُبايِعنَكَ عَلىٰ أَن لا يُشرِكنَ بِاللَّهِ شَيئًا وَلا يَسرِقنَ وَلا يَزنينَ وَلا يَقتُلنَ أَولادَهُنَّ وَلا يَأتينَ بِبُهتانٍ يَفتَرينَهُ بَينَ أَيديهِنَّ وَأَرجُلِهِنَّ وَلا يَعصينَكَ في مَعروفٍ ۙ فَبايِعهُنَّ وَاستَغفِر لَهُنَّ اللَّهَ ۖ إِنَّ اللَّهَ غَفورٌ رَحيمٌ

(Saheeh International)

O Prophet, when the believing women come to you pledging to you that they will not associate anything with Allāh, nor will they steal, nor will they commit unlawful sexual intercourse, nor will they kill their children, nor will they bring forth a slander they have invented between their arms and legs,¹ nor will they disobey you in what is right – then accept their pledge and ask forgiveness for them of Allāh. Indeed, Allāh is Forgiving and Merciful.

This is an allusion to pregnancy and childbirth, i.e., to falsely attribute a child (whether adopted or born of adultery) to a woman's husband.