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 a pillar within salah*

*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)

*The third proof is the hadith in bukhari 
"Whenever we offered prayer with the Prophet and he raised his head from the bowing, we used to remain standing till we saw him prostrating"*

This hadith is clear proof that the sahaba were looking infront of them and not to the place of prostration, and the sahaba wouldn't pray differently to the prophet SAW since he was the one who taught the greatest generation how to pray.

*Lastly, another proof from bukhari is 
"He (SAW) offered the eclipse prayer. His companions asked, "O Allah's Apostle! We saw you trying to take something while standing at your place and then we saw you retreating." The Prophet said, "I was shown Paradise and wanted to have a bunch of fruit from it. Had I taken it, you would have eaten from it as long as the world remains."*

Again this is clear proof of the sahaba looking towards the qibla. Its also a subtle indication that the prophet was also looking at the qibla as well,due to the fact that he was retreating (moving backwards) and he wouldn't have moved backwards if he was looking at the floor with his head down but rather he was looking in front of him which caused him to step backwards. And also the fact that he wouldn't have been reaching out for a bunch of grapes if he was looking at the floor but rather he would have been reaching out in front of him.

Juzakhullah, and hope this helps.