Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

Sujud al-Shukr is recommended for someone receiving a blessing from Allah or when an evil is warded off from him. It is also recommended when one sees somebody being tested with a chronic disease or being test by committing a sin. Abu Bakrah (may Allah be pleased with him), who said that when the Prophet (peace and blessings of Allah be upon him) heard any news that made him glad, he would fall down prostrating to Allah, may He be exalted.

According to the version narrated by Ahmad: he saw the Prophet (peace and blessings of Allah be upon him), when news reached him that his troops had prevailed over their enemy, he was lying with his head in `A’ishah’s lap, then he got up and fell in prostration.

Another hadith is that narrated by `Abd al-Rahmaan ibn `Awf, who said: the Prophet (peace and blessings of Allah be upon him) went out to the place where charity was kept, then he faced the Qiblah and fell in prostration, remaining like that for a long time. Then he raised his head and said, “Gabriel came to me with good news, he said, ‘Allah says to you, “Whoever sends blessings on you, I will send blessings on him, and whoever sends greetings of peace to you, I will send greetings of peace to him,”’ so I prostrated in thankfulness to Allah.”

Based on the explicit meaning of those reports, some scholars permitted the observance of Sujud al-Shukr even if a person in a state of ritual impurity. They include Ibn  Jarir al-Tabari, Ibn Hazm, Ibn Taymiyah, Ibn al-Qayyim, al-Shawkani and al-San`ani. But the massive majority of scholars maintained that it is like normal prayer which has to be offered in a state or ritual purity. I prefer the former view because it is in conformity with the explicit meaning of the report of Abu Bakrah which is quoted above.

Almighty Allah knows best.