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.
The narration reading, “The first one who will offer the funeral prayer for me is the Lord, may He be Glorified and Exalted, from above His Throne...” is a fabricated narration that was cited by At-Tabaraani (in Al-Muʻjam Al-Kabeer). Its chain of narration included ʻAbd Al-Munʻim ibn Idrees, who was known for being a liar. It was also cited by Ibn Al-Jawzi in his book Al-Mawdhooʻaat (The Fabricated Narrations).
Al-Haythami said, after quoting this hadeeth (8/605), “This was narrated by At-Tabaraani; and its chain of narration includes ʻAbd Al-Munʻim ibn Idrees, who was a liar and a fabricator.” [Majmaʻ Az-Zawaa'id]
As for the hadeeth cited by Imaam Ahmad perhaps you are referring to the marfooʻ hadeeth (i.e. a hadeeth that is directly attributed to the Prophet ) narrated by Ibn ʻAbbaas about the intercession on the Day of Judgment. It reads, “I will come to the gate of Paradise, take hold of its ring and knock on the gate. I will be asked, 'Who are you?' I will answer, 'I am Muhammad.' It will be opened for me; I will enter, and when I see my Lord on His Kursi - or Throne [Hammaad could not remember the exact word] - I will fall down 'saajidan, i.e. in prostration' before Him...” Shaykh Ahmad Shaakir declared its chain of narration saheeh (sound). However, it does not have the word 'jaalisan, i.e. sitting' that was mentioned by Imaam Ibn Al-Qayyim . Al-Albaani highlighted this point in his revision of the book Mukhtasar Al-ʻUluww, saying:
“Remark: In his book Ijtima'a al-juyoosh al-Islamiyyah, (Imaam) Ibn Al-Qayyim cited the hadeeth narrated by Ibn ʻAbbaas and reported by (Imaam) Ahmad with the following wording, '... and when I see my Lord on His Kursi - or Throne - 'jaalisan, i.e. sitting'.... The addition 'jaalisan' is not mentioned in the wording cited by (Imaam) Ahmad or by any other hadeeth compilers that we mentioned earlier. I believe that it is a mistake in the narration. I know of no authentic hadeeth stating that Allaah is sitting (on His Throne).” [End of quote]
It is not strange that a great scholar like Ibn Al-Qayyim might have cited a fabricated hadeeth or made a mistake regarding a word in a hadeeth; verily, only the Prophets of Allaah are infallible, and none of the scholars can be claimed to be infallible. Many hadeeth books compiled by great scholars of Islam cited fabricated ahaadeeth. Please refer to fatwa 85732.
The very hadeeth that you mentioned in the question was cited by the great hadeeth scholar Imaam At-Tabaraani in his book Al-Muʻjam Al-Kabeer. This does not undermine his great knowledge and status as a renowned hadeeth compiler in the slightest; even greater early scholars before Ibn Al-Qayyim have committed mistakes in narration. It is obvious that Ibn Al-Qayyim mistakenly assumed that the word 'jaalisan (sitting)' was included in the hadeeth and did not notice that the correct wording was “I will fall down 'saajidan (in prostration)' before Him.” This is why he stated in his famous poem An-Nooniyyah that the word 'jaalisan' was used in the hadeeth narrated by Ibn ʻAbbaas .
However, the followers of religious innovations, who hasten to defame and attack the scholars of Ahlus-Sunnah Wal-Jamaaʻah whenever any of them commits any given mistake out of confusion, should be asked about the other authentic pieces of evidence with clear indication cited by Ibn Al-Qayyim and others proving the istiwaa' of Allaah over His Throne (Rising over the Throne) and that He is above the heavens. What about the other pieces of evidence brought forth by the righteous predecessors proving this belief; are all these pieces of evidence fabricated and did Ibn Al-Qayyim make some additions to them to support his view as well?
Allaah knows best.