He only distinguished between them with respect to having caught any part of the prayer or not. There is no doubt that the one who lets the entire prayer time slip away is guiltier than the one who misses most of it, and the one who misses most of it is guiltier than the one who misses only a single rakʿah.

So we ask you: what exactly is this “catching” that occurs with a single rakʿah? Is it a catching that erases the sin?—no one says so. Or is it a catching that merely establishes the prayer’s validity? In that case there would be no difference between missing it altogether and missing all but one rakʿah.

67 – “Stand up for your master and help him dismount.” ʿUmar said, “Our Master is Allah, Exalted is He.” The Prophet replied, “Help him dismount,” so they helped him dismount.

Imam Aḥmad relates this (6/141–142) through Muḥammad ibn ʿAmr, from his father, from ʿAlqamah ibn Waqqāṣ, who said: ʿĀʾishah told me:

“I went out on the Day of the Trench following the people’s tracks. I heard the dull thud of the earth behind me—footsteps on the ground—so I turned and saw Saʿd ibn Muʿādh, with his nephew al-Ḥārith ibn Aws carrying his shield. I sat down on the ground. Saʿd passed by wearing an iron coat of mail whose edges were sticking out, and I feared for the parts of his body that were exposed. As he walked he chanted:

Would that the slow camel might reach the fray;
How fine is death when the appointed time draws near.

Then I rose and climbed over a garden wall. Inside I found a number of Muslims, among them ʿUmar ibn al-Khaṭṭāb, and with them was a man wearing a helmet. ʿUmar said, “What has brought you here?”