Valmiki Ramayana Sundara Kanda Sarga 57 Shloka 23
Original Shlokaसर्वथा कृतकार्योऽसौ हनुमान्नात्र संशयः।।5.57.23।। न ह्यस्याकृतकार्यस्य नाद एवंविधो भवेत्।
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असौ Oh that, हनुमान् Hanuman, सर्वथा always, कृतकार्यः successful, अकृतकार्यस्य if he was not successsful, अस्य his, नादः sound, एवंविधः in this manner, न भवेत् हि will not be so.
"Oh Hanuman is always successful. If he has not, he would not make sounds in this manner".