Heaping praise on West Bengal Chief Minister Mamata Banerjee for her austere lifestyle and political credibility, yoga guru Baba Ramdev on Saturday said the Trinamool Congress supremo could one day become Prime Minister."There should be no doubt regarding her credibility. Her image is clean. If Modi, a tea-seller's son could become Prime Minister, then Mamata Banerjee could also become Prime Minister," Ramdev told reporters outside Raj Bhavan after paying a courtesy call on Governor K.N. Tripathi.