Ibn Qudaamah's statement about laughter in prayer
31-12-2017 | IslamWeb
Question:
Assalaamu alaykum wa rahmatullaahi wa barakaatuhu. I was reading the following fatwa: https://www.islamweb.net/en/fatwa/298021
I have a question about the quotation from Ibn Qudaamah, where it mentions, “If a person laughs and two letters are articulated, his prayer is valid, as well as if one laughs boisterously even without two letters.” Does this not contradict what was mentioned in the latter part of the excerpt from Al-Mughni, where he mentions that Ibn Al-Munthir said, “The scholars unanimously agreed that laughing invalidates the prayer, and most of the scholars hold that smiling does not invalidate it.” I am definitely missing something very important here, so please clarify!
Answer:
All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no contradiction in the statement of Ibn Qudaamah in his book Al-Mughni. He said at the beginning, “If he laughs and two letters are articulated, his prayer is invalid, as well as if he laughs boisterously even without the two letters (being articulated).” After that he said, “Ibn Al-Munthir said, ‘The scholars unanimously agreed that laughing invalidates the prayer.’”
The statement of Ibn Al-Munthir is interpreted to mean that the prayer is invalidated by laughter if two letters are articulated. An-Nawawi 
said, “According to our School (Shaafi‘i), smiling does not affect the validity of the prayer, nor does laughing if less than two letters are articulated; however, if two letters are articulated, the prayer is invalid. Ibn Al-Munthir reported the consensus of the scholars that the prayer becomes invalid by laughing, but this is understood to mean if two letters (or more) are articulated...”
Hence, there is no contradiction between the statement of Ibn Qudaamah and the statement which he attributed to Ibn Al-Munthir at the end.
Allah knows best.