Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: The Prophet (peace and blessings be upon him) did not have any woman who had gifted herself to him. On the basis of this hadith, if its chain is sound, it is as though the Prophet (peace and blessings be upon him) deferred marrying them and did not accept them, even though they were lawful for him (peace and blessings be upon him). And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13356