The Book of Marriage
Ṣaḥīḥ Muslim 3464
الْمُؤْمِنُ أَخُو الْمُؤْمِنِ فَلاَ يَحِلُّ لِلْمُؤْمِنِ أَنْ يَبْتَاعَ عَلَى بَيْعِ أَخِيهِ وَلاَ يَخْطُبَ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَذَرَ
al-muʾminu akhū al-muʾmini falā yaḥillu lilmuʾmini an yabtāʿa ʿalā bayʿi akhīhi walā yakhṭuba ʿalā khiṭbah akhīhi ḥattā yadhara
Transliteration generated from the Arabic vowel marks
The full narration
Uqba b. 'Amir said on the pulpit that Allah's Messenger (ﷺ) said:A believer is the brother of a believer, so it is not lawful for a believer to outbid his brother, and he should not propose an engagement when his brother has thus proposed until he gives it up
Source
Ṣaḥīḥ Muslim · 3464
Ṣaḥīḥ