Is it sufficient to say the closing salam once, and the scholarly disagreement on this matter

Question : And among the topics of research regarding the salam is if one limits it to a single salam. Is that sufficient?

Answer : This is also a point of disagreement among the scholars. Some say it is sufficient, citing the hadith of Aisha: "He used to conclude the prayer with the salam."
This is an absolute expression that applies to a single instance. Others said it is not sufficient, and that the "al" in "al-salam" refers to the mental concept, meaning the known salam, which is "Peace be upon you and Allah's mercy" to the right and "Peace be upon you and Allah's mercy" to the left.
They cited as evidence for this his statement in the hadith narrated by al-Nasa'i, which we referred to earlier: "It was sufficient for any one of you to say 'Peace be upon you' to the one on his right and the one on his left." They said that what is less than the minimum requirement is not sufficient or permissible, because if he said "this is sufficient for you," it means that what is less than it is not sufficient. This is the well-known position of the Hanbali school, that both salams are necessary and it is not permissible to omit them. They also cited the Prophet's (peace and blessings be upon him) consistency in performing both salams. They said that his consistency in doing so, whether present or traveling, in the presence of Bedouins, Arabs, the knowledgeable, and the ignorant, indicates that they are necessary. This is supported by his statement: "Pray as you have seen me praying."
Some scholars said that one salam is sufficient in voluntary prayers but not in obligatory ones. This is because it was reported from the Prophet (peace and blessings be upon him) that he said one salam facing forward in the witr prayer. They said that voluntary prayers may be lightened in ways that obligatory ones are not. Accordingly, one salam is sufficient in voluntary prayers but not in obligatory ones. These are three opinions: Is it necessary to say both salams in obligatory and voluntary prayers, as is the well-known position of the school? Or is one salam sufficient in both obligatory and voluntary prayers? Or is one salam sufficient in voluntary prayers but not in obligatory ones?
In any case, the precaution among the three opinions is best. That is to say the salam twice. Because if he says it twice, no scholar will say his prayer is invalid. If he says it once, some scholars will say his prayer is invalid. It is known that the Prophet (peace and blessings be upon him) commanded precaution in matters where the evidence is not clear. He (peace and blessings be upon him) said: And he (peace and blessings be upon him) said: And if you perform the second salam, you have performed a remembrance by which you draw near to Allah (Mighty and Majestic) and you are safe from being told that your prayer is invalid. Those who said that both salams are obligatory in obligatory and voluntary prayers said that the action of the Messenger (peace and blessings be upon him) is a specific case that may involve forgetfulness or something else, so this action is not preferred over the statement that said "It was sufficient for any one of you to say such and such." However, there is a consideration regarding this possibility, because the default for the action of the Messenger (peace and blessings be upon him) is legislation and not forgetfulness, especially since he said one salam facing forward, contrary to custom, which indicates that he intended it deliberately. But as I said, the precaution is to say the salam twice in obligatory and voluntary prayers.