Q; is placing ur hands below the navel against the sunnah or ijma of sahabas?
A; All-Praise is due to Allah,
In Imam An-Nawawwi in Sharih Al-Muslim (The Explanation of Muslim) [4/115] said, The hadeeth of Ali (may Allah be pleased with him) he said: It is the Sunnah to pray by placing your palm on the other palms below the navel.
This is Da'eef (Weak) and has been agreed upon it grading of weakness, narrated in Hadith Daaraqutni and al-Bayhaqi narrated from Abu Shaybah Abdul Rahman ibn Ishaq Wasti who is considered a weak narrator and the Scholars agreed upon it's weakness. End of Quote.
Albaani said, The hands should be placed on the chest only; there is no difference between men and women in this regard. I say: placing them anywhere other than on the chest is da’eef (weak) or has no basis. End of quote,
(Albaanis Description of the Prophet Prayer from the takbir to the Taslim)
Just to confirm this the agreement of it's weakness the Scholars graded it as follow's-
Abu Dawoud said, in his narration of this Hadith no: 758, There is in the chain narration Abdul Rahman ibn Ishaq Al-Koofi and I heard Imam Ahmad say's he is weak.
Al-Buyhaqi said in his book Sunnan Al-Kobora No: 2/31,
It's chain narration is weak.
Ibn Qahtaan said in his book Al-Waham Al-Ehaam no: 5/26, In this Hadith is Ziyaad Bin Zaid who we dont know, and Abdul Rahman ibn Ishaq Wasti who Ibn Hanbal and Abu Haatim say's about him, his Hadiths are Munkar (Denounced rejected)
An-Nawawi said in his book Majmooa'h no: 3/313, From the narations by Abdul-Rahman ibn Ishaq Wasti, That has been graded weak by the consensus of the Scholars.
Adh-Dhahabi said in his Tanqeeh Al-Tahqeeq no: 1/140,
Hadith is not correct (untrue).
Ibn Kathir said in his book Al-Ahkaam Al-Kabeer no: 2/362, It's weak.
Ibn Hajr Al-Asqalaani said in his book Fatih Al-Baari no: 2/262, Weak chain narration.
Ash-Shawkaani said in his book Neel Al-Awtaar no: 2/203, Weak Hadith.
Albaani said in his book As-Silsilat As-Sahihah no: 1/211, Weak Hadith.
These are just some of the Scholars that mentioned this Hadith as being weak and there is many more but I mentioned the names who are most renowned amongst the Scholars of Hadith. The correct way of placing the right over the left in Prayer is in the Hadith of Ibn Khuzaymah authenticated by Albaani and narrated by Waail Ibn Hajar that I Prayed with the Messenger of Allah (peace be upon him) and he placed his right hand over his left hand on his chest .
So the conclusion to your question is yes it is against the sunnah and consensus of Scholars due to the wide range of evidences that are available.
And Allah knows best....