The source said on Saturday that military intelligence had searched al-Bashir's home and found suitcases loaded with more than $351,000 and six million euros ($6.75m), as well as five million Sudanese pounds ($104,837).
"The chief public prosecutor... ordered the [former] president detained and quickly questioned in preparation to put him on trial," the source said.
"The public prosecution will question the former president in Kobar prison," the source added.
Relatives could not be reached on Saturday for comment about the investigation.
Al-Bashir, who is also being sought by the International Criminal Court over allegations of genocide in the country's western Darfur region, was removed on April 11 by the military following months of protests against his rule.
His family said this week that the former president had been moved from the presidential palace to the high-security Kobar prison in Sudan's capital, Khartoum.
As president, al-Bashir often played up his humble beginnings as the child of a poor farming family in Hosh Bannaga, a small village consisting mainly of mud houses on the eastern bank of the Nile some 150km north of Khartoum.
The Sudanese Professionals Association (SPA), which has spearheaded the protests, has called for holding al-Bashir and the members of his administration to account, a purge of corruption and cronyism and easing an economic crisis that worsened during al-Bashir's last years in power.
On Wednesday, Sudan's ruling military council ordered the central bank to review financial transfers since April 1 and to seize "suspect" funds, according to state news agency SUNA.
|Sudanese protesters chant slogans during a rally outside the army headquarters in Khartoum [Ebrahim Hamid/AFP]|
The council, which has resisted calls by protesters to hand over power to a transitional civilian body, also ordered the "suspension of the transfer of ownership of any shares until further notice and for any large or suspect transfers of shares or companies to be reported" to authorities.
Members of the protest movement said five of its representatives were due to hold talks with the military council at 8:00pm local time (1800 GMT) on Saturday to discuss the transfer of power.
Ahmed al-Rabia, an SPA member, said if the military rulers refused to hand over power, then the protest leaders would go ahead with their planned announcement of a "sovereign civilian council" on Sunday.
"If they are willing to negotiate, then there is a chance that tomorrow's announcement could be postponed," Rabia told the AFP. "What we want from them is a timetable to hand over power, so things don't drag."
Since al-Bashir's removal, the military council has held two rounds of talks with the protest leaders, he said, adding: "During these talks, we've felt that the military council has no desire to hand over power."
The military council and Moussaka Faki Mahamat, chairman of the African Union Commission, also met in Khartoum on Saturday. The AU has warned Sudan's military rulers to hand over power to a civilian body by the end of April or risk suspension.
Al Jazeera's Hiba Morgan, reporting from Khartoum, said Mahamat met the council on Tuesday as well.
"The African Union Commission has been very clear since the military council took over from President al-Bashir that they do not agree with the military takeover and they're saying that unless the military council hands over power to an independent civilian transitional government, then the revolution of the people will be incomplete and Sudan would risk losing its membership in the African Union," she said.
Meanwhile, thousands of protesters continued their weeks-long sit-in outside the army headquarters in Khartoum, demanding a civilian-led transition.