مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 3144
Marriage
Making a Marriage publicly known, asking Woman in Marriage, and the Condition laid down - Section 1
وَعَنْ أَبِي هُرَيْرَةَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَا يَخْطُبُ الرَّجُلُ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَو يتْرك»
Abu Huraira reported God’s Messenger as saying, “A man must 'not ask a woman in marriage when his brother has done so already, until he marries or gives her up." (Bukhari and Muslim.)
Mishkat al-Masabih, 3144مُتَّفَقٌ عَلَيْهِ (الألباني)