Leaving a dead body with something heavy in water

Abu Abdullah (asws) questioned me: ‘What was the place in which you placed (the body of) Zayd?’ I said, ‘There were three issues. As for one of them, so there were very few of us who were left behind with us, but rather, we were eight persons. As for the other one, so we were afraid from the morning, which would have exposed us. And as for the third, so it was his bed (resting place) which he proceeded to’. So he (asws) said: ‘How far was the Euphrates from the place in which you placed (buried) him?’ I said, ‘A stone’s throw away’. So he (asws) said: ‘Glory be to Allah (azwj)! So why did you all not tie a (piece of) iron to him, and throw him in the Euphrates, and that would have been preferable?’ I said, ‘May I be sacrificed for you (asws), no, by Allah (azwj), we had no way for this’. So he (asws) said: ‘Which thing (were you on) on the day you all came out with Zayd?’ I said, ‘We were Believers’. He (asws) said: ‘Who were your enemies?’ I said, ‘Infidels’. He (asws) said: ‘I (asws) found in the Book of Allah (azwj) Mighty and Majestic: "[47:4] So when you meet in battle those who disbelieve, then smite the necks until when you have overcome them, then make (them) prisoners, and afterwards either set them free as a favour or let them ransom (themselves) until the war terminates”. You all began by evacuating yourselves from captivity. Glory be to Allah (azwj)! You did not have the ability to travel with the justice even for a while’.