What is the ruling on When a person dies while his son was abroad and he was adviced to go alone to his father's grave and pray Salat al-Ghaib how far is that true please clarify with authentic Hadith.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is permissible to perform the funeral prayer on a deceased person until one month after his burial, if one had not performed it on him. This is the opinion of the majority of Muslim scholars.

Ibn Qudaamah wrote in his book Al-Mughni: “If one misses offering the funeral prayer on a dead person, he may perform the prayer as long as the body is not buried. If it is buried, he may even offer the prayer until one month after the burial (but after that period no prayer is to be performed on the grave). This is the opinion of the majority of Muslim scholars. Therefore, you are permitted to offer the prayer on your dead father as long as his burial date has not exceeded one month.

Allah knows best.