Sayyidah Aishah (may Allah be pleased with her) says: I asked the Prophet (peace and blessings be upon him) about a young girl whose family marry her off: should her permission be sought or not? He (peace and blessings be upon him) said: "Yes, her permission should be sought." Then Aishah (may Allah be pleased with her) said: But she feels shy and stays silent. So he (peace and blessings be upon him) said: "That is her permission, when she stays silent."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13703