A man is, Alhamdulillah, very much involved in Tabligh Jamaat work.

Answer

You should offer him naseehat. Explain to him that deserting his parents whilst they are suffering and dependent on him, is haraam – absolutely haraam. His prior and Waajib 'tabligh' is the khidmat (service) of his aged and ailing parents. He closes the Portals of Jannat for himself by his callous abandonment of his aged parents. Rasulullah (sallallahu alayhi wasallam) said: "Your father is your central Portal of Jannat. If you wish destroy it or if your wish guard it."

Allah Ta'ala has bestowed Aql to a man. He should utilize his intelligence to understand that he is grossly disobedient and trampling on the huqooq (rights) of his parents. In the circumstances it is haraam for him to abandon his parents even if the objective is tabligh. An intelligent man is one who is able to distinguish between two good deeds and to select the deed of greater importance. This applies when both options are open for selection. But, in the case of this man, he has no option. The choice is between halaal and haraam. It is haraam for him in the circumstances to go for tabligh.

Once a man came to Rasulullah (sallallahu alayhi wasallam) and sought permission to participate in Jihad. When Rasulullah (sallallahu alayhi wasallam) was informed that he had an aged mother, he (Nabi – sallallahu alayhi wasallam), refused permission and said that his Jihad was to remain in the service of his mother.

What is mentioned in Ahsanul Fataawa is correct. Whilst this deserter of parents labours under the delusion of being in the Path of Allah, he is under the Wrath of Allah Ta'ala for the zulm he has inflicted on his aged, sickly parents. He is behaving like an animal which does not recognize its parents. According to the Hadith merely looking at the face of parents is the equivalent of a Maqbool Hajj. The thawaab of remaining in the service of such ailing aged parents as you have described is millions of time superior to going out for tabligh. May Allah Ta'ala guide your him. May Allah Ta'ala grant him the taufeeq to understand that he is perpetually under the Wrath of Allah Ta'ala as long as he persists with his zulm of desertion. He has deserted and abandoned his aged and ailing parents in their time of dire need. He is a most ungrateful son. This type of evil conduct towards parents can lead to an evil Maut. Transgressing the limits of the Shariah is evil extremism (ghulu') which is haraam. Whenever the limits of the Shariah are transgressed, the consequence is corruption and deviation from Siraatul Mustaqeem. Excess is haraam.