All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Going out for the purpose of calling people to Allaah is one of the best acts of worship by which one gets nearer to Allaah. Allaah Says (what means): {And who is better in speech than he who [says: "My Lord is Allaah (believes in His Oneness)", stands straight (acts upon His Order)] invites (people) to Allaah's Islamic Monotheism, does righteous deeds, and says: "I am one of the Muslims."}[Quran 41:33]. Furthermore, the Prophet said: "I swear by Allaah! If Allaah guides one single man (to Islam) by your efforts, that will be better for you than possessing an abundant number of red camels (a very expensive breed of camels)." [Al-Bukhari and Muslim] For more benefit about going out with the Tableeghi group, please refer to Fatwa 83288.
Nonetheless, a person who wishes to go out for the purpose of calling people to Allaah is obliged to provide for the people who are under his guardianship, and he should secure for them a safe accommodation, because if one is negligent in this, he has not fulfilled the trust he was entrusted with. The Prophet said: "All of you are guardians, and all of you will be questioned about those under his guardianship." [Al-Bukhari and Muslim] Moreover, the Prophet said: "It is enough a sin for a man to neglect those under his guardianship." [Ahmad and At-Tirmithi] For more benefit, please refer to Fataawa 85929 and 86003.
As regards the period during which a man is permitted to be absent from his wife, whether he was in Da'wah (calling people to Allaah), business, or else, the scholars differed in opinion in this regard. Our view in Islamweb is the period which 'Umar determined which is six months; for more benefit, please refer to Fataawa 90778 and 88642.
Allaah Knows best.