How sound is the Hadith: "The gates of heaven are opened, and supplications are answered in four instances: when ranks meet [in battle], when rain falls, when prayer is being established, and upon seeing the Kaaba"? And did some scholars act upon it, despite your mention in Fatwa no. (11932) that there is no evidence for the answering of supplications upon seeing the Kaaba? And is this authentically attributed to the Prophet, peace and blessings be upon him?

The hadith (definition) that refers to the opening of the gates of heaven and the acceptance of supplications upon seeing the Kaaba is very weak and not authentically attributed to the Prophet, peace and blessings be upon him. This is due to two defects: the weakness of "Ufayr ibn Ma'dan" and the tadlis (deceptive narration) of "Al-Walid ibn Muslim."

Some scholars have acted upon this hadith despite its weak chain of narration, such as Imam Al-Shirazi, while Imam Al-Nawawi commented that it is a gharib (uncommon) hadith that is not established.

As for the desirability of supplicating upon seeing the Kaaba, a group of scholars, including Ibn Qudamah, held this view, citing what was narrated from Ibn Abbas and Ibn Umar regarding raising hands when facing the Kaaba. However, this hadith is not authentically marfu' (attributed directly) to the Prophet, peace and blessings be upon him; the correct view is that it is mawquf (attributed to the Companions).

Imam Al-Shafi'i mentioned that raising the hands upon seeing the Kaaba is good, and Imam Ahmad indicated its desirability. Accordingly, there is a permissible difference of opinion regarding supplicating upon seeing the Kaaba, even if nothing specific regarding it has been authentically established from the Prophet, peace and blessings be upon him.