Ibn Umar (Allah be pleased with them) said that Allah's Messenger (ﷺ) prohibited Shighar which means that a man gives his daughter in marriage on the condition that the other gives his daughter to him in marriage with- out any dower being paid by either.

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى عَنِ الشِّغَارِ ‏.‏ وَالشِّغَارُ أَنْ يُزَوِّجَ الرَّجُلُ ابْنَتَهُ عَلَى أَنْ يُزَوِّجَهُ ابْنَتَهُ وَلَيْسَ بَيْنَهُمَا صَدَاقٌ ‏.‏