What is meant by "Al-Harj" in the noble Hadith: "Worship in Al-Harj is like emigration to me," and is it correct to write "صلي" (salli) or "صلِ" (salli) when supplicating for the Prophet?

The Hadith: "Worship during times of turmoil (harj) is like migration to me" is an authentic Hadith narrated by Muslim and others from Ma'qil ibn Yasar. "Harj" refers to tribulation and the disruption of people's affairs. The reason for the merit of worship during such times is that people become heedless of it. As for sending blessings upon the Prophet, peace be upon him, using the past tense, its form is "ṣallā." The short alif (alif maqṣūrah) is omitted from it in the state of connection (waṣl) due to the meeting of two quiescent letters, so it is pronounced "ṣal."