Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) forbade that any of you sell over the sale of another, or propose over the marriage proposal of another, until the one who proposed before him withdraws or gives him permission.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14032