Castro said Maduro had promised to visit him soon when he wished him a happy 88th birthday on August 13.
The leader of the island's communist revolution said Maduro had made the visit on Tuesday during a "foreign trip regarding the defense of his country's major oil interests."
"I congratulated Maduro for his extraordinary solidarity with the heroic people of the Gaza Strip," said the 88-year-old leader, who handed power to his younger brother Raul in 2006 because of ill health.
"The genocide being carried out in the Gaza Strip... Is one of the most dramatic events" in history, he said, calling Israel "a nuclear power that is at once sophisticated and irresponsible."
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"The chaos in world politics has become evident. That's why my meeting with the Venezuelan president was so useful," he added.
Since his retirement, Castro has devoted himself to writing articles and receiving foreign dignitaries. In July he met Russian President Vladimir Putin and Chinese President Xi Jinping when they visited the island.
Maduro, the political heir of late socialist leader Hugo Chavez, has maintained the tight alliance his mentor forged with Cuba, which depends heavily on oil-rich Venezuela's largesse.