Humza Yousaf has described how his brother-in-law, a hospital doctor in the Gaza Strip, has seen “death and destruction” in the ongoing war.
Mr Yousaf said his brother-in-law was in a “terrible way” as he continued to treat patients in southern Gaza.
The parents of the First Minister's wife Nadia El-Nakla were visiting relatives when war broke out between Israel and Hamas, leaving them trapped in Palestinian territory for weeks amid heavy shelling.
They managed to return to Scotland earlier this month after being allowed through the Rafah border crossing into Egypt.
The Prime Minister was asked about the state of his family as he spoke on BBC Radio 4's Broadcasting House program on Sunday.
His in-laws are still recovering from the ordeal, he said, adding: “In all honesty, I didn't think I would see them again as time went on.
“There was one particular call that I will never forget as long as I live.
“My mother-in-law called at around 1.30am saying they had been told their neighbour's house was going to be targeted and so there was no doubt the blast would hit them.
“She started saying goodbye and I'll never forget her telling me to watch her girls.”
The Prime Minister said he exchanged messages with his brother-in-law, who works almost non-stop, on Saturday.
Mr Yousaf said: “He says he has never seen death and destruction like this before.
“He told me he doesn't know how he's going to recover from this.
“He said one of his first jobs when the conflict started was trying to match the body parts to the right body.
“It's in a terrible way.”
He called for a ceasefire but acknowledged that it would take “incredibly hard” work.
His comments came after thousands of protesters marched in Glasgow in support of the Palestinian cause.
Those who took part in Saturday's march were asked to write their names on their hands as a gesture of solidarity with the besieged population of Gaza, who used the method so they could be identified and buried with relatives if killed.
On Tuesday, the Scottish Parliament will debate calls for a ceasefire in the Israel-Hamas war.
Scottish Labor leader Anas Sarwar said he and his party would support a ceasefire when it comes to a Holyrood vote, a position which differs from that of Sir Keir Starmer.
He told BBC Scotland's Sunday programme: “I support the ceasefire.
“I support an end to rocket fire into and from Gaza, the immediate release of hostages, immediate access to humanitarian aid and a path to a peace process.
“I would like the Labor amendment (in the House of Commons) to go further than last week and include that call for a ceasefire.”