The Maliki madhab stresses that the worshiper looks towards the qibla at all times during salah,
If the worshiper looks at the place of prostration then his head bows down and his standing will be incomplete.(since he is not standing straight) *And standing up straight is considered an obligation within salah.
Here is the list of proofs that the malikiyyah bring forward.
*the first proof is the quran verse.
Allah subhanahu wa ta’ala says, “…wheresoever you people are, turn your faces (in prayer) in that direction (Al-Masjid al-Haram).”*
Imam qurtubi in his tafsir states that ****"In this verse is clear proof for what Malik and those who agreed with him that the worshiper should look in front of him, not at the place of his prostration."
The second proof is from the authentic narration in which the prophet SAW taught the bedouin how to pray he said
"stand up until you are standing straight".*
Due to this hadith Ibn al-arabi states: "so if one looks down to the place of prostration he will neglect standing up straight in prayer with his head (faced down)
He also states that if one was to keep there head straight but look down, this would cause immense discomfort. And nothing is made difficult within islam.
*Lastly, another proof from bukhari
when the Messenger, alaihi as salaatu was salaam, prayed As-Salaatul Kusuuf, he informed his companions that he was shown Jannah and the Hell-fire, so he said to them “that is when you saw me moving forward and moving backwards”.
This hadith is clear proof that one looks in the direction of the qibla during salah, the prophet knew the sahabas gaze were placed in the direction towards him and brought this to their attention. this would mean the prophet (SAW) also prayed this way since it is known in the famous sahih narration where he states "pray as you have seen me pray"
This hadith also proves that the prophet was looking towards the qibla as well, since he was moving away and also towards what was infront of him, this can only mean he was looking in that same direction (towards the qibla). And to move forwards and backwards with his head down looking at the floor is nonsensical.
Juzakhullah, and hope this helps.