Yes, according to the Vinaya Atthakathā:
Sace dve atthi, dvepi āpucchitabbā.
“If both exist [i.e. are alive], then leave must be obtained from both.” — Vin-a. v. 1011
But the atthakathā also gives a number of exceptions. Here’s a translation I made of it some years ago. We can see that articles 11 and 12 offer two ways of getting around the rule, though I’ve never heard of anyone actually attempting it.
(1) Here, the phrase “from his mother and father” was said in regard to the man and woman who conceived him. If both are living, then leave must be obtained from both of them.
If the father or mother is deceased, then leave must be obtained from [the parent] who is still living.
Even if they have themselves gone forth, leave must still be obtained from them.
(2) When obtaining leave, he may either go and obtain it himself, or may send another person, saying to him, “Go to my mother and father and having obtained their leave come back.”
(3) If he says, “I am one who has obtained permission,” he may be given the going forth if it is believable.
(4) A father has himself gone forth and wishes his son to go forth; having obtained leave of the mother, let him go forth; or, a mother wishes her daughter to go forth; having obtained leave of the father, let her go forth.
(5) A father, not concerned for the welfare of his wife and son, runs away. The mother gives her son to some monks, saying, “Let him go forth.” When asked, “Where has his father gone?” she replies, “He has run away to disport himself.” — It is suitable for him [the son] to be given the going forth.
A mother has run away with some man or other. The father gives [his son to some monks, saying], “Let him go forth.” The principle in this case is just the same as above.
The Kurundī* states: ‘A father is absent. The mother gives her son permission, saying, “Let him go forth.” When asked, “Where has his father gone?” she replies, “I shall be responsible for whatever is due to you from the father.” — It is suitable for him [the son] to be given the going forth.’
[* Kurundī: one of the Sinhalese commentaries most frequently cited by Buddhaghosa as the source of his Vinaya exegesis.]
(6) The mother and father are deceased. Their boy has grown up in the company of [relatives] such as his maternal aunt. When he is being given the going forth, his relatives start a quarrel or criticize it. Therefore, in order to stop the quarrel, he should obtain their leave before being given the going forth. But if given the going forth without having obtained their leave there is no offence.
They who undertook to feed him in his childhood are called “mother” and “father”, and with respect to these the principle is just the same as above. The son [is reckoned as] one living dependent on himself, not on a mother and father.
(7) Even if he be a king, he must still obtain leave before being given the going forth.
(8) Being permitted by his mother and father, he goes forth, but [later] reverts [to being a householder]. Even if he goes forth and reverts seven times, on each occasion that he comes [to go forth] again he must obtain leave [from his mother and father] before he may be given the going forth.
(9) If [his mother and father] say: “This [son of ours], having reverted and come home, does not do any work for us; having gone forth he will not fulfil his duty to you; there is no point in him obtaining leave; whenever he comes to you, just give him the going forth.” When [a son] has been disowned in this way, it is suitable for him to be given the going forth again without even obtaining leave.
(10) He who when only in his childhood had been given away [by his mother and father, saying], “This is a gift for you; give him the going forth whenever you want,” may be given the going forth whenever he comes [to ask for it], without even obtaining leave.
But [a mother and father], having given permission [to their son] when he was only in his childhood, afterwards, when he has reached maturity, withdraw their permission; he must not be given the going forth without obtaining leave.
(11) An only son, after quarrelling with his mother and father, comes [to the sangha, saying], “Let me go forth.” Upon being told, “Come back after you have obtained leave,” he says, “I’m not going! If you don’t let me go forth, I shall burn down your monastery, or stab you with a sword, or cause loss to your relatives and supporters by cutting down the plants in their gardens, or kill myself by jumping from a tree, or join a gang of robbers, or go to another country!”
It is suitable to let him go forth in order to safeguard life. If his mother and father then come and say, “Why did you let our son go forth?” they should be informed of the reason for it, saying, “We let him go forth in order to safeguard life. You may confirm this with your son.”
(12) Then, [one saying] “I shall jump from a tree,” has climbed up and is about to let go with his hands and feet. It is suitable to let him go forth.
(13) An only son, having gone to another country, requests the going forth. If he had obtained leave before departing, he may be given the going forth.
If he had not obtained leave, having sent a young monk to get [the parents] to give their leave, he may be given the going forth. If it is a very distant country, it is suitable to just give him the going forth and then send him with other bhikkhus to inform [the parents].
But the Kurundī states: ‘if [the country] is far away and the way to it is [across] a great wilderness (or desert), it is suitable to give him the going forth, [thinking], “having gone there [later] we shall obtain leave [of the parents].”’
(14) If a mother and father have many sons and speak thus: “Venerable sir, may you give the going forth to whichever [one] of these boys you choose,” then having examined the boys, he may give the going forth to the one he chooses.
If an entire [extended] family or an entire village is given permission [by someone, saying], “Venerable sir, may you give the going forth to whichever [one] of the boys in this family or this village you choose,” he may give the going forth to the one he chooses.
(Samantapāsādikā. v. 1011-12)
