"...If the party liable is mentally deficient, or weak, or unable Himself to dictate, Let his guardian dictate faithfully, and get two witnesses, out of your own men, and if there are not two men, then a man and two women, such as ye choose, for witnesses, so that if one of them errs, the other can remind her. The witnesses should not refuse when they are called on (For evidence)." - Quran 2:282 (read more)

"Narrated Kurib: the freed slave of Ibn 'Abbas, that Maimuna bint Al-Harith told him that she manumitted a slave-girl without taking the permission of the Prophet. On the day when it was her turn to be with the Prophet, she said, "Do you know, O Allah's Apostle, that I have manumitted my slave-girl?" He said, "Have you really?" She replied in the affirmative. He said, "You would have got more reward if you had given her (i.e. the slave-girl) to one of your maternal uncles." - Sahih Bukhari 3:47:765 (read more)

"Due to the differences of both lives the Prophet (Sallallahu Alaihi wa Sallam) is not aware of what is going on in this world. He does not know who is asking help from him, and who is seeking child, wealth, wife, etc. ... On the other hand, if it is said that the Prophet (Sallallahu Alaihi wa Sallam) is alive in his grave, it does not mean that his life is similar to the life of those who are living in this world. So, if one seeks his help asks something from him he commits Shirk (polytheism)." - IslamWeb