What are the situations in which the opening Takbir (Takbirat al-Ihram) is caught with the Imam, and is it permissible to commit some forbidden acts to attain the virtue of maintaining it for forty days?

The jurists differed on the precise criterion for attaining the takbīrat al-ihrām (opening takbīr). Some said: It is attained by engaging in the takbīr immediately after the Imam's ihrām, provided one is present for his takbīr. Others said: By attaining a part of the standing. And still others said: By attaining the beginning of the bowing. Some scholars held that it is attained by saying the takbīr before the Imam begins reciting the Fātiḥah. Al-Shanqīṭī was of the view that the criterion is to attain the takbīr before the Imam starts reciting the Fātiḥah. If the prayer is silent, then it is estimated by the time it takes for the Imam to recite the duʿāʾ al-istiftāḥ (opening supplication). Accordingly, if the worshipper attains the takbīr with the Imam before he starts reciting, he has attained the virtue; otherwise, he has missed it. The worshipper should not pray while needing to relieve himself, nor should he rush his walking to attain the takbīrat al-ihrām; rather, he must maintain calmness and dignity. As for saying the takbīr without being in the row to attain the virtue of the takbīr with the Imam, the jurists have not mentioned anything concerning it except what the Malikis stated regarding the fear of missing the rakʿah.