Prayer is the most important symbol of Islam; Allah emphasized its importance when He chose the heavens to be the place where He enjoined it upon our Prophet Muhammad (blessings and peace of Allah be upon him) during his ascent into heaven (Mi‘raaj). And He also emphasized its importance when He first enjoined it upon His Prophet Moosa (peace be upon him), when He spoke to him alone on the right side of al-Toor, and said to him (interpretation of the meaning): “Verily, I am Allaah! Laa ilaaha illa Ana (none has the right to be worshipped but I), so worship Me, and perform As‑Salaah (Iqaamat‑as‑Salaah) for My remembrance” [Ta-Ha 20:14].
He emphasized its importance when He made it the foundation and pillar of faith. Whoever neglects it will be more neglectful of other duties, and whoever prays regularly, it will be light and a protection for him on the Day of Resurrection. Hence it is the main aspect of the straight path and the one of the fundamentals of the true religion, as Allah says (interpretation of the meaning): “And they were commanded not, but that they should worship Allaah, and worship none but Him Alone (abstaining from ascribing partners to Him), and perform As‑Salaah (Iqaamat‑as‑Salaah) and give Zakaah, and that is the right religion” [al-Bayyinah 98:5].
If the Muslim recognizes the importance of prayer in the Islamic religion and have respect in his heart for what Allah has enjoined of honouring the symbols of Allah, as He says (interpretation of the meaning): “Thus it is an obligation that mankind owes to Allaah] and whosoever honours the Symbols of Allaah, then it is truly, from the piety of the hearts” [al-Hajj 22:32], then he will realize that distracting one who is praying and trying to make him laugh or move or speak is a kind of tampering with what is sacred, and there is the fear that the one who does this will come under the heading of those who mock the symbols of Islam, which is one of the causes of falling into apostasy, Allah forbid. The Prophet (blessing and peace of Allah be upon him) said: “If the one who passes in front of one who is praying knew what (sin) he incurs, he would realize that waiting for forty is better than passing in front of him.” The narrator, Abu’l-Nadr, said: I do not know whether he said forty days or months or years. Narrated by al-Bukhaari (510) and Muslim (507). What level of sin is incurred by the one who deliberately distracts one who is praying or tries to make him laugh by moving or speaking? There can be no doubt that it is a grave sin.
The hadeeth mentioned in the question is not saheeh, and is not narrated in the books of Sunnah and reports. Rather Imam Ahmad (may Allah have mercy on him) said: There is no saheeh hadeeth about laughing [i.e., in prayer]. End quote.
Al-Tahqeeq fi Ahaadeeth al-Khilaaf, by Ibn al-‘Jawzi, 1/198
Shaykh Ibn Jibreen (may Allah have mercy on him) was asked the following question:
How sound is the hadeeth, “Whoever makes a praying person laugh has made Allah weep”?
The hadeeth with this wording is not saheeh, but there is no doubt that if you are talking to one who is praying and making him hear words until he starts to laugh and thus invalidates his prayer, you are the cause of that. It is not permissible to make a praying person laugh and the like. End quote.
Shaykh Saalih al-Fawzaan (may Allah preserve him) was asked the following question:
Is it narrated in the Sunnah that “Whoever makes a believer laugh whilst he is praying has made one thousand angels weep”? If it is not saheeh, then what is the sin that results from that?
I do not know of any basis for this hadeeth, but it is not permissible for the Muslim to distract his brother whilst he is praying or to make him confused about his prayer. If a person can prevent one who wants to walk in front of him when he is praying, and there is a stern warning concerning that, then it is more appropriate that the stern warning should apply to the one who makes him laugh and distracts him from praying. The one who passes in front of a person who is praying may have a need to do that, but there is no need to joke and make a praying person laugh, and to distract him from his prayer. So the one who does that incurs a great deal of sin. End quote.
And Allah knows best.