Hadith.3458 - It is narrated by al-Ala', from Muhammad ibn Muslim, from one of the Imams (as), peace be upon them, regarding a man who frees his male or female slave as a mudabbar (to be freed after his death) and then becomes in need of the slave's price.
Imam (as) said
"No, he may not sell the slave-unless he stipulates to the buyer that the slave must be freed at the time of his death."